- One of the most common trouble calls for HVAC
- Basic checks of the thermostat to see if it is broken or?
- The basics of the thermostat
- Learn what a heating anticipator is and what type of thermostat uses them.
- Fixing a Broken Thermostat
- Finally, lots of related useful links to help you learn your HVAC system
Troubleshooting Broken Thermostats - The main connection between the air conditioning and heating system and the end user is the thermostat. Beyond the air conditioning and heating thermostat, many people know nothing about the HVAC systems that keep them comfortable year round.
There comes a time when the thermostat has a problem or the end user wants to replace the thermostat because they think it is a broken thermostat. It is not uncommon for a person to call an HVAC contractor and tell the secretary that they think the thermostat is broken because their air conditioner or heating system does not work.
Fixing a Broken Thermostat | Professional Help
In some instances, this is the case while in others the thermostat is not broken but something is wrong with the air conditioning and heating equipment that needs to be repaired. In either case, it is usually best to call an HVAC professional to look at the problem especially if you want to replace the thermostat. There are a few things you can check with your thermostat before you call an HVAC professional. Therefore, a little thermostat troubleshooting is in order.
Troubleshooting Broken Thermostats
What To Check
- An air conditioning and heating thermostat, even if it is a digital thermostat, is simply a temperature switch that turns the air conditioning and heating system on and off. As with any switch, it needs electricity to function or cause a function with the air conditioning and heating equipment. Most residential and light commercial thermostats are powered by 24 volts A.C. The thermostat gets this 24 volts A.C. from the air conditioning and heating equipment. Usually, this power comes from an air handler in an air conditioning and heating split system and from the main unit for air conditioning and heating package systems.
Power Switches and Circuit Breakers
- Check the circuit breaker for the air handler or furnace to make sure it is not tripped. Also, check the power switch which should be located near the air handling unit. It is not uncommon for people to mistake these switches for a light switch and turn them off. They unknowingly just turned the power off for their air conditioning and heating equipment including their thermostat. That is when they begin to think they have a broken thermostat. If you have a digital thermostat the power display and the thermostat power display light may not function if you have this problem. Some air conditioning and heating thermostats use batteries to power the back light which takes us to number two in air conditioning and heating thermostat troubleshooting. Check the power switch and breaker to ensure the power is on before assuming you have a broken thermostat
Fixing a Broken Thermostat
The back display light for the digital thermostat does not function but the air conditioning and heating system works fine. Check the batteries as some digital thermostats require AA or AAA batteries for the back light to function on the thermostat.
The back display light for the digital thermostat does not function but the air conditioning and heating system works fine. Check the batteries as some digital thermostats require AA or AAA batteries for the back light to function on the thermostat.Types of Digital Thermostats
There are two main types of digital thermostats; Digital thermostats that use batteries for the back light to function and digital thermostats that use the power from the air conditioning and heating equipment. If you don’t know which kind of air conditioning and heating thermostat you have then opened the thermostat up and look inside. If you don’t see any batteries or a battery compartment inside the thermostat then your thermostat uses power stealing technology. It is probably an older model digital thermostat. If it is a programmable thermostat then every time you lose power you will lose the program inside. Finally, this takes us to the next step in air conditioning and heating thermostat troubleshooting.
- Power Problems
- Location
- Drafts
- Anticipators
- Mechanical Thermostats
The Program is Gone
Fixing a Broken Thermostat
The programmable thermostat is always losing its program. This is most likely one of the older thermostats that use the power from the HVAC equipment. Additionally, every time you lose power you lose the program inside the thermostat. Furthermore, programming a programmable thermostat can be a chore for many people to figure out. Therefore, a problem like this can be frustrating especially if you live in an area where there are constant power failures.
The only solution to this problem is to replace the programmable thermostat with one that uses power stealing technology. This type uses power from your HVAC system to hold the programs. Additionally, it has a battery back-up just in case you lose power. Lastly, this can save you lots of trouble and frustration. Finally, it keeps you from reprogramming the thermostat over and over again when power failures occur.
If the problem is persistent with the thermostat it is important to get back to thermostat basics.
Fixing Broken Thermostats - The Basics
Location
Is the thermostat installed in the proper location? This is very important as a thermostat installed on a wall that has high heat gain or heat loss will never offer you comfort as it will react mostly to the temperature of the wall and not the air in the living space. Additionally, thermostats installed where direct sunlight can hit the thermostat is going to be a problem also. Furthermore, a thermostat located near an outside door or window will be affected every time the door or window is opened or closed.
A thermostat should be located close to the return (where the filter is installed) so that it senses and reacts to the air returning to the air handler for conditioning. Additionally, thermostats located near heat sources like hot or cold water pipes, radiant heaters, fireplaces, electrical devices which produce heat, etc… will never offer accurate temperatures and conditioning for the room(s).
Drafts
Is there a big hole behind the thermostat that will feed cool or warm drafts to the back of the thermostat? All thermostats have a hole behind them where the wires come into the thermostat from the air handling unit. Check this and if you find a big hole behind the thermostat stuff some insulation in this hole and cover it with a piece of tape. Finally, this will prevent drafts from affecting the thermostat.
Anticipators
Has the heating anticipator been properly set by a qualified air conditioning and heating technician? The heat anticipator is on mechanical non-digital thermostats. Additionally, it needs to be set according to the amp draw on the heating control circuit. The heat anticipator offers a small amount of energy savings and prevents thermostat overshooting for you. Furthermore, it shuts off the main burners because the fan will continue to run and dissipate the heat.
The heat that remains in the furnace or heater. Digital and programmable thermostats have built-in heating and cooling anticipators. They automatically set themselves with no manual adjustments. The mechanical thermostat needs a manual adjustment. You need a tool called an amp meter to determine the proper setting. Finally, the cooling anticipator in the mechanical thermostat requires no manual adjustment.
Mechanical Thermostats
Fixing a Broken Thermostat
If you have a mechanical thermostat with a mercury bulb switching mechanism inside it this thermostat needs to be level. If the thermostat is not level you never get an accurate temperature in the residence or business.
Other problems that can occur with your air conditioning and heating thermostat. Those other problems need to be discussed with an HVAC professional. Furthermore, these problems can be technical and require special tools to fix. It is always a wise choice to call in an HVAC professional when you have problems with your air conditioning and heating equipment, Lastly, that includes your air conditioning and heating thermostat.
Troubleshooting Broken Thermostats
how do you check to see if the thermometer itself is faulty? I have a digital thermometer that now always reads 74 degrees. When it’s hot outside the unit runs constantly an eventually shuts off and blows hot air. When it’s cool the temp remainws 74.
If it always says 74 then something is wrong. Check the temperature by using a temperature sensor you know to be reliable to check the temperature near the thermostat. If its bad replace. And it is possible you could have more than one problem there. Call a professional to have it checked out.
I honestly don’t think it’s your t state. Sounds more like it’s low on charge and when it blows warm air, your compressor is kicking off on thermal overload
This information is helpful and I did learn some. However, I need further trouble shooting. My thermostat is digital with batteries powering the backlight, it has options for heat, cool and fan. Until recently, I was able to take the cover off and “reset” the thermostat so the A/C would kick back on. Now only the fan works, even after several resets and battery changes. Is it my thermostat or an HVAC issue?
From what you are describing Kayla I would say it sounds like an HVAC issue. Best thing to do at this point is to call in a pro to check it out. Good Luck!!
You replaced the batteries and the back light won’t come on what are you do?
Call a professional or replace the thermostat.
I have a strange question. We moved into a new house June 6 and it has geothermal heating and cooling. I don’t know anything about these systems. for 2 1/2 weeks it was on 73 and stayed 73 worked great. we did not touch anything because we did not want to mess it up. From out of nowhere it started getting hotter in the house the temp is 80 at times almost unbearable. We had a guy who works on them come out said the air going in fine and temp out fine. He does not no what the problem might be asked me turn down to 70 and leave it. He said keep eye on light on side when I see any lights above green one let him know. I wonder if the thermostat might not be working correctly. I am so hot last night it was colder outside than in here I opened windows in my room. It was fine before I don’t understand what changed. Please give me advice! Should I call a different person to look at it. By the way lights not changed. I swear think warm air comes out sometimes it is too hot in here.
Thanks
Sherrie
It could be anything and yes I recommend you call someone who specializes in geothermal systems. I am guessing your system has a refrigerant leak and it is freezing up sometimes. When it is not cooling you will experience reduced airflow from the vents. Call someone who specializes in this type of system and they will set you straight. And I am only guessing your system has a leak from the symptoms you describe. To be absolutely sure call a geothermal specialist.
We have a digital thermostat that uses power stealing, no battery backup. The thermostat constantly needs to have the time reprogrammed on it (5+ times daily) and sometimes the display goes blank. Heater kicks on/off according to programming just fine. Have verified the circuit breaker is not tripped and the power switch is on. Has our thermostat gone bad? What else can we verify or should we call an hvac technician to have it replaced?
Yes………….it is time to be replaced and preferably with one that has a battery back-up. I have had this type of thermostat before and it is a pain to reprogram every time there is a glitch in the power system.
Honeywell RTH110B thermostat. The digital display is on…fan set to auto. Last night it did not come on at set temp (72)..display shows it is 79. Checked air handler cb …ok. Do I have a thermostat concern or unit in attic.
Thanks in advance.
Not enough information provided to make an solid assessment. The best thing to do at this point is to call a professional to check it out.
The temperature display on the thermostat shows only one digit. How do we fix it?
replace the thermostat
My thermostat will not show anything on the display what can be wrong . And the Air Conditioner is not working !
I can only guess but you most likely have a problem with power somewhere. Check the breakers and switches for the inside unit. Follow the instructions here before calling an HVAC contractor to repair the problem.
We just bought a brand new a/c unit because our old one needed to be replaced as it would constantly only put out cool air. The new one was working for a week before it started to put out cool air again. It is set at 73 degrees as the display shows, but the display says it is 81 degrees in here. I cannot figure out if the thermostat is the issue.
call the installing company. It should be under warranty.
My thermostat got hit and the digital screen is broke, that happen a few days ago now the air ant working just the fan in the house I guess, the outside fan ant working… Anyone know what I should do.
Replace the thermostat
My temperature control does nothing. Can’t turn it off, set temperature, nothing you touch will respond. This is a Honeywellcontrol for my Rheem 3 ton unit.
Power problem or the thermostat is bad are the likely causes.
I sprayed disinfectant spray onto the a/c screen that displays the degree number temperature. But now the display is mingle with numbers and words. Will the screen of the thermostat return to normal after it drys? I’m too afraid to tell my parent. ? ):
As with many electronics a thermostat is susceptible to getting wet inside. If you are lucky it will dry out and return to normal operation but it is also likely it is damaged and needs to be replaced.
I have to keep turning thermostat on and off for it to work. Is it the thermostat? Evert once in a while you hear it click and it comes on.
Just guessing as you did not provide much information but it is likely something wrong with the HVAC system.
I have a gas ac package unit the ac has never had a problem , but now the heat will run fine 85% of the time and then randomly not come on after the thermostat clicks. If i reset the breaker it will come right back on. Also it seems to work fine on program, mainly does it when i use the hold button.
Sounds like you need to have a technician look at the unit before you press the button to reset it. Only guessing but it likely an ignition problem and that needs the attention of a trained and qualified technician.
Dear Sir I have a Totaline 8 button programable thermostat. The LCD is reading -HP and bounces back and forth to the normal screen displaying tempature and mode. Unit is currently not working.
The HP with Totaline thermostats typically means it is in Heat Pump mode. If the unit is not running then likely there is a problem with the equipment and not the thermostat.
We have a heat pump and on the display inside the house we have a reading for the outside temp. That number says that it is 103 degrees outside and in reality it is 24 degrees outside. This isn’t the thermostat for the house, this is just the reading for the outside temp. What can I do about this? Is it something that I need to be worried about?
Sounds like the temperature sensor needs to be replaced. Technically it is called a thermistor. It is important that this device be installed properly. The thermistor or outside air temperature sensor needs to be installed where no other heat source can cause it to read incorrectly. eg……a dryer vent, a flue, or even in the direct sunlight can cause it to read incorrectly. Additionally, the correct type of wire needs to be used in running the the wire from the thermostat to where the thermistor is located. The wire should 16 or 18 gauge shielded wire as other wiring can have cause incorrect readings. All these things need to be considered including the thermistor can go bad over time for various reasons. Additionally, if the programming in the thermostat ties into the controlling the outside unit when the temperature drops then you will have a problem if the system is an air source heat pump and the thermostat is programmed to turn off the outside unit when the temperature drops below the programmed set point and use the inside back up heat source. Call your local HVAC contractor and have them check it out.
I have a thermostat that is set to 72 degrees but on the left it shows its 14 degrees in the house. What do u think the issue is
Not sure? What kind of thermostat? Has the set up inside the thermostat been changed to Fahrenheit for all settings?
My programmable thermostat is not showing the word aux. the pump does turn on and airhandler. But the 2nd stage heatt does not kick in to help.
The second stage or auxiliary heating (commonly referred to as back-up heating for a heat pump) should only kick in when there is an offset in temperatures. For example, if it is extremely cold outside the air source heat pump will not get enough heat from the air outside to keep up with demand (actually the homes or structures heat loss). The thermostat temperature reading will slowly continue to drop. Typically, depending on the thermostat set up, when the temperature falls 3 degrees Fahrenheit below the current set point only then will the auxiliary heating kick on (via a thermostat command). On some thermostats the offset is adjustable so that can be narrowed to say 2 degrees or expanded to to say 4 degrees. There could also be another problem that needs the attention of a technician to check out. Turn the thermostat setting up by three degrees to see if the auxiliary heating comes on. If it does there is not a problem.
Hello, I recently had my thermostat replaced. Shortly afterwards I had to have my furnace repaired. The thermostat worked fine up until then. Now it seems to be having issues. The thermostat no longer displays heat on when the furnace is running and the furnace seems to run longer now. Any suggestions? Thanks in advance.
Sounds like an anticipator problem but it could be something else. Is it an older mechanical type of thermostat? If so then there is a manual setting for the heating anticipator inside the thermostat. This would cause the furnace to run longer or shorter depending on the anticipator setting. An HVAC technician can set it for you. The setting is based on the amperage draw of the heating control circuit and requires a special meter to read that amperage draw. Newer digital thermostats are set automatically.
I just replaced an older digital honeywell thermostat that kept shutting off due to low battery. Each time I would replace the battery in that previous unit, it would sometimes work fine for months, other times only for a few hours and then the low battery indicator would start again. Where we live, sub zero temps outside right now mean that a few hours without heat drops the temp inside pretty drastically. We woke up with the temp inside at 59 because the thermostat had shut off sometime during the night. I assumed that it was going bad so I replaced it with a new Honeywell digital thermostat with brand new batteries. It had been working for about 4 hours when all of a sudden the low battery indicator showed up. Could it be bad wiring going from the thermostat to the furnace? Any suggestions?
Not sure whats going on there. Most thermostats are powered by the low voltage transformer that should be located inside the HVAC equipment. I couldn’t tell you exactly what it is but it is probably a very good idea to call in an HVAC tech to properly troubleshoot the problem.
I have a Carrier HVAC unit with digital thermostat. Purchased unit in June 2009. Currently on 5th compressor, replaced coil at 6 mos. Thank God I Purchased 10 yr parts & labor warranty. But now having problem w/thermostat. Set on 65. Furnace just keeps running, have to adjust temp down to get unit to cut off. And while it was cold here couple days temperature fluctuates on thermostat from 64 to 65 causing auxiliary heat to come on. Opening the cover to reset temp can also trigger temp displayed to show lower temp when cover opened. My heat ran nonstop last night & today while at work. Have never replaced thermostat with all other problems. What is “life” of thermostat typically? Does this sound like thermostat problem? Sorry to be long winded. PS I hate this HVAC unit. Thank you for your help
I’ve seen antique thermostats work just fine along with newer thermostats. Many times, people think something is wrong with their thermostat when it is really the equipment. The temperature has been extremely cold recently so, from what you are describing, it is possible there is nothing wrong with the system all. It is simply trying to keep up with the heavy demand placed on it from the cold weather. Most HVAC systems, when installed properly, take into account an average degree day for the area where you reside. When temperatures go to the extreme then your system will work overtime to keep up. Without being there to check it out and only going by the information provide I can only make assumptions here but I have been on trouble calls (in extreme temperatures) where I found nothing wrong with the system. I can only recommend to the people to add more insulation or consider getting their house wrapped and have old doors and windows replaced. Weather-proofing your home can go a long ways in saving the energy your HVAC system produces. The average degree day is one factor mentioned above for properly sizing your system……………some other factors involved in properly sizing the system are materials and insulation in the home. These are used for heat loss and heat gain calculations. I am only surmising your system is working properly. If you are uncomfortable call your HVAC contractor to check it out.
Hello Richard,
I just had a sensor replaced that had burned out on the furnace. Ever since, the Honeywell Digital non-programmable thermostat (no model number) keeps resetting itself to 75 degrees every few hours. Have tried new batteries, shutting it off and on, etc., but nothing will make it hold a setting for more than a short time. Do you know of any way to make it stop resetting, or do we need a new thermostat? Thank you!
The power for most thermostats comes from the furnace or air handler. That, in most furnaces and air handlers, is where the transformer is that provides power for the low voltage circuits in your HVAC system. I would check to make sure that the thermostat has not been programmed to some obscure setting. After that I would cycle the power off and on to the furnace or air handler and see if the thermostat held its setting. If not then, barring no other checks for your particular system, I would replace the thermostat.
My thermostat is acting crazy its flashing all kinds of things. The unit is running but blowing cold air!?!? Please help
Please call an HVAC contractor to fix this. Don’t be cold. As cold as the weather has been recently the cold can become dangerous and even cause severe damage to your home by freezing the pipes and such.
My Lennox thermostat has suddenly started changing time on the program to 12pm or so after I reset program and it runs awhile. Reverts to 12 pm setting. What is solution
It could possibly be a power issue but it could also be that the thermostat is going bad. Best to call your local HVAC contractor and have them check it out. There are switches near the air handler or furnace that look like wall switches and some people mistake these for light switches. If you turn that switch off it will kill power to the air handler and the thermostat. The switches are not always clearly marked so make sure no one is turning that switch on and off again. While the thermostat should have a small back up battery inside it these batteries need to be changed from time to time. I think most Lennox thermostat have a small round battery inside them kind of like you find in a watch or a computer. Try changing that battery……it could be the problem.
I have a question about my digital thermostat. I like to keep the temperature set @ 72°, but for some reason the temperature goes up to 84°, ( only when my daughter come home ) can the set temperature of 72° go up by itself. Or someone is messing with the control panel.
I would suspect someone wants the temperature to be higher. It could also be a programmable thermostat and it is set to change at a specific time. So before you point any fingers figure the model and manufacturer and download the instructions for the thermostat unless, of course, you have the instructions for the thermostat somewhere. There are newer programmable thermostats that can be programmed and locked with a PIN # so only people with the PIN # can change anything on the thermostat.
My Bryant thermostat keeps blinking HP don’t know what the problem is outside compressor will not kick on
The HP is an error code but I am not 100% familiar with Bryant error codes so I am only guessing. If the outdoor unit is not kicking it is possible the unit kicked off because of “head pressure” which could be the problem with your unit but I am not 100% certain because it could be something depending on Bryant’s error codes. A head pressure problem is a problem with the condensing unit outside and it means you have a problem with the refrigeration system. A couple of issues involving this could be condenser fan motor failure or the coils are blocked from passing air through them. There are some other more technical issues that it could but it is probably best that you call an HVAC contractor to solve the problem for you as I never recommend a homeowner opening up the cabinet to their condenser as there is high voltage in there and you really need to know what you are doing when you are inside the unit.
It is a protection feature in the diagnostics of the air conditioner or heat pump to protect the system from excessive pressures. Sometimes this issue is caused by lack of maintenance or a part failure of some kind.
Have a trane tstat and the display will go blank for a little while and then comes back on. It will do this sporadically and when the display goes off the air handler comes on but the outside unit does not kick on and as soon as the display comes back on the air handler shuts off. Any ideas could it possibly be the tstat it is an older unit approximately 10 years old.
I can’t say without looking at that problem.
Hi, My thermostat works correctly except for the fan on/auto button. On auto it works as expected. If I switch to ON to have the fan run continuously – nothing happens. Is this a thermostat problem? thanks
It is possible it is a wiring problem but it could also be something with controls in the air handler. It is probably best to call an HVAC contractor to solve this issue.
Thank you for the help..we are experiencing an issue with our a/c unit. It will run and cool the house but if we flip it off at the thermostat the fan will cycle on and off by itself..we have checked the contactor, it’s fine! our thermostat is a digital battery operated (Honeywell) Does this sound like a possible thermostat issue?
Not sure about that one. Does your thermostat or system have a ventilation mode (although some manufacturers can call it something else)? If you do not know the answer to that then you have to read the user manuals for both the thermostat and the HVAC unit. This feature is usually only found on high end equipment for residential systems.
Yesterday I attempted to install a Nest. When I turned the power back on, the unit was not getting power via through the low voltage wires. I then reattached the old thermostat thinking I had done something wrong on the Nest install and now it is not getting power as well (it had worked fine before turning off/on the power). I put batteries in the old thermostat and the AC is now not responding to being tuned on and the temp turned down. Is there an additional breaker near the unit or something else that “trips” when you turn off the power? Next to the compressor there is box with a large fuse in it that has two finger holes and when you pull it out there is are slots for two small copper rectangles. Does this need replaced? Thank you very much for your help.
Sounds like you blew the transformer which provides low voltage control power for the system. It is best to call a professional to fix this for you. This usually happens when you do not kill the main power to the air handler when you change the thermostat. Then when you are handling the wires you accidentally create a dead short and it blows the transformer. Hopefully the transformer was fused and you don’t have to replace it. You simply have to replace the blown fuse. Again, there is high voltage in the air handler and I always recommend a professional do this.
Thank you so much. Will call the pros in tomorrow. Have a great week.
For future reference, do I need to flip the “light switch” that is above the handler under the house, or pull the 120 V fuse that is near the compressor on the wall outside before attempting this? Or do I just need to not touch the low voltage wires that go into the thermostat? Thanks again.
I explain this in other articles that have to do with replacing or installing a new thermostat. You can do what you describe or you can simply go to the circuit breaker panel and kill the circuits for both the condenser and the air handler. The control transformer is most often found in the air handler but I have seen some in the condenser so it is best to kill both to avoid any problems. The air handler and the condenser should be on separate circuits in the breaker panel.
my husband cleaned around our central a.c. unit and now nothing will work. no heat no air not even the fan. and we replaced the thermostat with a Honeywell® Mercury Free Thermostat (YCT87N1006) about 4 months ago
is the new thermostat bad?
Your comment went into the spam folder for whatever reason and we do not check the spam folder that often. Anyhow, I am guessing it is probably not the thermostat but something he did when cleaning around the unit. Maybe bumped into some wires or something like that. It is probably a good idea to call in a professional HVAC contractor to figure it out as you are dealing with electrical stuff. I am hoping you already figured out the problem or a contractor already figured out the problem.
I have 2 units. My upstairs thermostat went blank and no air is on. I swapped the face plate for the one downstairs to see if it was the thermostat or HVAC.It was fine downstairs, however the one I moved upstairs was initially stuck at 77 degrees (obviously incorrect) and about an hour later went blank. My thermostats do not have battery back-ups. I tried turning the thermostat off and then turning back on to see if it made a difference, and also checked the circuit breaker with no change. Any other relatively easy checks I can do before calling my HVAC technician? I had a preventative maintenance visit in early April and was told everything looked fine.
no, if the circuit breaker is good then you should probably call a pro to see what the problem is. I am only assuming but guessing your air handler for the upstairs unit is in the attic??? I had a call like this one time and somehow a squirrel got into the attic probably through the soffit somewhere and chewed on the thermostat wire which has a brown jacket so it can look like a tree branch I guess. I don’t know, I try not think like a squirrel but am only guessing. Sorry I couldn’t help you any further.
I live in a 55 and older apartment complex where the maintenance man seems to know nothing about hvac except to add freon. Mine has leaked down 2 times in 3 weeks. The thermostat flashes ‘cool’. I have turned the unit off to reset it.I tell the manager he is wasting freon and letting it loose in the atmosphere.
What should I tell the manager is wrong with the unit, I doubt she will bring in a qualified technician. He does not take the covers off and look at anything. I do not know how he got license,IF he has any.
Don’t know what to say here except to maybe get a third party contractor to look at it which would likely require the managers approval and they will likely require you to pay for the third party service. I’m not pointing fingers or playing any blame game but sometimes the maintenance guy has his hands tied because management doesn’t want to spend the money to replace old outdated equipment so he does the best he can with the budget he has. I’m not saying that is the case here but it happens all too often.
I have a very simple Honeywell thermostat. Dual system, upstairs and downstairs. Both units worked great all winter for heating, but do not work with the AC. Upstairs, the thermostat shows 85 (or some other high number) when AC has been running for hours. I have an separate indoor thermometer which reads below where I have set the thermostat. Downstairs, I set thermostat at 72 and AC continues to run even when the thermostat shows it is 68 in the house and I am wearing a sweater. I want to try replacing the thermostats since these were cheap units, although they are only 2 years old. Think I’m on the right track? What throws me is that they both worked perfectly all winter for heating. Thank you.
I’m guessing it is not the thermostat but rather something else wrong. I know you did not mention it but do you have heat pumps and if so how old are the systems? I seriously doubt your thermostats will will resolve your problem. Sorry about giving you this news but I suspect you have another issue that will require the services of a professional to look at and fix. Additionally, if these are not heat pumps have you checked the outdoor units (condensers) to make sure they are running when you call for cooling?
Hello. I have called for service. There’s no heat pump. Agree with you it cannot be the thermostats because what’s the chance both units would malfunction at the same time? My furnace is only two years old, the AC could be much older. It does run. The house is cooled beautifully, but the AC just never shuts down. Many thanks. I’ve learned quite a bit by visiting this site.
Here is an article that will help you with that problem………………of course it never hurts to have a professional look at the system and give it a check over to make sure everything is running well. I am only assuming the following article will help you with your problem so calling in a professional will make double dang sure. Beating the Heat – Helping Your Air Conditioner is a good place to start for you.
I have a Honeywell mercury/dial unit. The heat works well in the winter months, but the air doesn’t seem to shut off In the summer. I have the thermostat set at 76 degrees and even though the temperature in the house is 72 degrees, the airconditioner still remains on. The only time it shuts itself off is if the temp is set above 80 degrees. Do I need a new thermostat?
I think it is a good idea to call a professional. You probably have something wrong with the cooling in your AC.
Our Honeywell thermostat says external temp is 127 degrees even during a blizzard! Now when AC shuts off, red light comes on upper left side and Error 53 flashes.
You have a bad thermistor or in layman’s terms a bad outdoor air temperature sensor. Not sure about the error code 53 but likely it has something to do with the bad thermistor. Disconnect the bad thermistor and see if the code goes away. You can replace this thermistor yourself or call a pro to do it. It may or may not require running a new wire for the outdoor air temperature sensor and the wire should be separate from the regular thermostat wire. It needs to be twisted pair shielded wire for you to get accurate temperature readings. If the wire is not the correct wire then that also could be your problem especially if the wire for the thermistor is near other wires.
These things are sensitive to the electromagnetic waves that are derived from other wires so it must be shielded wire for the thermistor otherwise you will not get accurate readings. You likely do not need this sensor as sometimes it is simply for the convenience of knowing the outside air temperature. However, depending on your system and how the thermostat was setup, your system may rely on an accurate outside temperature to work properly. This is especially true for heat pumps. To check if this feature is enabled you need the installers manual which is usually easily found on the internet for whatever thermostat model number you have there.
when I turn on the AC or heat the set point does not appear on my thermostat and the AC / heat does not turn on. This happened last week, and was temporarily fixed by resetting the breakers and changing the thermostat batteries. Those simple fixes are now not working. Is it the thermostat or the AC unit?
From what you say here I would say its the thermostat. The only real way to tell is to jump out some of the terminals to tell. If you are careful and want to do it yourself take a small jumper wire (I use them with alligator clips on the end) and jump between the R terminal and the G terminal. If the indoor fan comes on that is good. Then jump between the R and the Y terminals. If the outdoor condenser comes on it is good. Then jump between R and W. If the heat comes on then that is good. If all these work then the thermostat is bad and needs to be replaced. If they do not come on when you jump out the described terminals then something is wrong with your HVAC system and you need to call a pro. Hope it works for you.
I have a digital power robbing thermostat. In the past month or so, the thermostat will not always trip the inside fan (blower) to turn on. When I realize its not working, I have to reset the thermostat in order for it to turn the fan back on. I hired AC tech and they keep saying I need to replace the whole AC system. I am assuming they are doing this to upsell me.
Have you ever seen this issue before? Please Help
Can’t say for the AC without looking at it but if it is more than 15 years old then its probably time to go. However, as long as it isn’t costing you a lot in repair bills and is reliable I guess it’s okay provided you don’t mind the unit being inefficient. Why did the AC Tech not find the problem with the fan? I am only guessing (because I have not looked at the system) but your problem is likely with the equipment and the thermostat.
The system is 9 years old. As it relates to the tech, he replaced what looked like a battery, and states thats probably the issue. I did not see him look at the thermostat. When the thermostat trips the fan, I can hear a click. In the instance I have no fan, I dont hear the click from the thermostat.
I can’t help you. There simply is not enough information. Call a competent HVAC repair company and tell them to fix the problem. They should fix the problem before recommending anything.
I have seen wiring issues similar to this. If you have a meter and can check the wiring from the thermostat to the blower fan you can check a couple things that may help you out in the long run. One check the voltage to the switch in the furnace that activates the blower fan. You should have a solid 24Volts from the thermostat to the furnace area…..If it is 19 VDC or lower, It could be the wiring. A short someplace or broken copper strands in the wire may be creating to much resistance. Sometimes those switches are finicky and they wont operate at lower than 22 VDC or so. IF you do find the voltage to be low, Run a new proven good wire from the thermostat to the furnace…and see if that fixes the issue. If not its probably the thermostat. Im not an AC tech so take anything I say with a grain of salt. But I have worked industrial maintenance for 25 years or more if that helps any?
My thermostat will not set above 37.5 it won’t let me set it at 65 because it won’t go up pass that number never had a problem I think my daughter was messing with it but now I can’t get it back to normal I took the battery’s out I’m not sure if that’s how u rest it
sounds like it was changed to Celsius. Change it back to Fahrenheit.
I have been having a problem with my thermostat. It doesn’t seem to be running the set program and is always heating up the place to 78 degrees or higher. I have to run the AC for a few hours to cool the place, even if outside temperate is cool like in the 60s. The thermostat has been programmed to hold temperature at 70 but is always way hotter than that.
Probably best to call an HVAC contractor to check it out.If the program is correct then you likely have a problem with the equipment.
Carrier 4 button tstat–Thermoglow backlight has never worked (this is a non-battery tstat). I have gone to step 9 in advanced setup–says backlight is on, but it is not. This is for a heat pump.
What do you think–possible wiring problem?
This is a 6 wire tstat–Red/Hot (R); Green (G) air handler; Yellow (Y1) compressor; White (W2) back-up heat strip; Orange(BOW1) reversing valve; Blue (C) common.
No, think its the thermostat. The back light is likely the malfunction.
Hi. I have an electric furnace. When I turn on my Honeywell thermostat it just blows cold air and continously read the temp as 64F. I reset the breakers at the main panel and the furnace but still only blows cold air even if i up the temp to 80 on the thermostat
its likely a problem with the furnace and not the thermostat. Call a contractor for troubleshooting and repair.
I have a Honeywell CT70A thermostat. Lately, the heating will work for a few minutes and then stop, never reaching my temp. set point. No breakers are being tripped. Could the thermostat be faulty?
Doubt it……………..it sounds like something is wrong with the furnace but to be absolutely sure you need to call an HVAC contractor to check it out. Make sure you have clean filters and all your supply vents are open so you have good air flow. Blocked air flow will cause problems like you are describing.
I had my A/C & heating unit completely replaced about 2 weeks ago. When they replaced everything they replaced the thermostat too.. with the exact same one (Honeywell FocusPRO 5000 Series). Within a week it told me to replace the batteries. I have gone out and purchased at least 20 new batteries and it keeps saying replace batteries. Sometimes it will work fine for 24-48 hours before saying “replace batteries”. I’m just wondering if it is a faulty thermostat…any help is appreciated.
You need to call the installation company back and have them replace the thermostat. It sounds like it is a bad thermostat and it should covered under the installations company warranty.
I have our thermostat set to 64 degrees and twice in the last week I woke to 60 degrees. After removing the cover for the thermostat and switching from manual to program and back to manual the furnace kicked on and worked fine. As soon as I put the cover back on it kicks off. I have repeated the process and all works fine if I leave the cover off. I suspect a fault in the circuit board that is activated by the slight compression from the cover. Thoughts?
First, check to make sure no wires are loose where they make the connection to the thermostat. If everything is good these then yes, I would say it is likely the thermostat is defective in some way. In that case, replace it.
our trane furnace is 3 years old. the first year we owned it the circuit panel in the furnace was bad. the thermostat is a honeywell. It is battery operated digital thermostat, also 3 years old. i just changed the batteries and furnace filter 3 weeks ago. Today the display is blank. I tried changing the batteries and the filter, checked the circuit breaker and am not at a loss as to what might be wrong. I think this furnace is a lemon. Possible? And of course it’s over Thanksgiving weekend.
If you have a multimeter you can test between hot and common (typically the red wire and the blue wire) and see if you have 24 volts. You may also use a single jumper wire and jump the red and green terminals…………if the blower fan comes on the its the thermostat and not the furnace. If it doesn’t then you have lost control voltage and/or main power to the furnace. I’ve seen many different scenarios from old thermostat wire shorting out the control circuit (in that case it should be fused but you need to find the short first before replacing the fuse……….if it is not fused then the transformer is blown), to squirrels chewing through the wire, to someone driving a nail in the wall and hitting the wire, and many other possibilities. Running basic tests as described will isolate the problem so it can be repaired. It may not necessarily be the furnace.
I have a battery backup. The low battery words were blinking, so I changed the battery and it continues to blink even with two different sets of fresh batteries. Thoughts?
replace that thermostat.
I have a Honeywell thermostat that is programmable. It has a battery, which is new. I program it for different settings, hit run. It runs fine, but always reads 71 (furnace), temperature and setting. (at 5 pm, it is supposed to be 73, at 10 pm, supposed to be 70). It just stays at 71. If I hit hold, I can change it to whatever I want. 71 is an okay temp, but something is wrong with it, that it won’t hold a program.
Yep, I’ve seen this before and is usually resolved with a new thermostat. Something is wrong with that thermostat.
I am trying to find a replacement for an old thermostat, but can’t find one with the right settings. My current (very) old thermostat is for a water boiler furnace, 3-wire. Thermostat is for heat only – but my furnace needs a heat call and also a “heat off” call. I cannot find any thermostats that will send a call to turn the heat off. Any suggestions for a model that could do this?
A thermostat is nothing more than a switch that closes the contacts on a call for heat. When the temperature is satisfied the contacts open killing the 24 volt power thus shutting down the system. Usually that 24 volt power goes to a relay that turns a circulator on and off for the boiler and the boiler typically controls itself using its own temperature control located inside the boiler. It is probably best to call a pro so they can determine what you have and make suggestions about it. They may know exactly what you have there after looking at it and can offer a solution for you.
I have a round mechanical thermostat (COOL/OFF/HEAT, FAN ON/AUTO) which disregards the desired temperature and acts as if it is stuck at 80+ degrees. The only way to disable the heater is to switch from HEAT to OFF. There is no apparent problem with the thermistor, because it displays the correct temperature of the room. Any suggestions would be greatly appreciated.
It is possible the white and red wire are touching each other somewhere. It could be bad wire insulation in the wiring jacket or it could be that someone drove a nail in the wall and that caused the issue. The only way to tell is to ring out the wires with an ohm meter when they are disconnected at both ends. That is disconnected from the thermostat and the furnace. If you get continuity in the wires when they are separated and disconnected then you need to replace the wire which can possibly be a big job and best left to a professional.
We have our Rodger white thermostat set for 69 degree. Before the heat comes it, the temperature on thermostat drops 2-3 degrees. The heat then will go to the set temperature. Is it normal for the for the temperature to drop the 2-3 degrees? The thermostat is approximately 12 feet away from our garage door entrance and cold air does come into the house when we open the door.
not exactly what model you have there but some thermostats have a way to calibrate or offset the temperature to bring it closer to what you desire. If you do not have the paperwork for that thermostat then you can look it up on the internet. It’s White-Rodgers which is now owned by Emerson Electric.
My Emerson Sensi thermostat turn on and off perfectly for the AC. However, for some reason the heat turn on and does not turn off, driving the temp inside the house very high. It is a gas furnace if it helps. I replaced the batteries and checked the wires:
RH=red
O/B=white
Y=yellow
G=Green
W/E=blue
The heat worked perfectly with a basic thermostat a year ago before this one was installed. Could it be the thermostat?
I’m thinking it is a wiring issue. Recheck the wiring and make sure none of the bare copper is touching and other wire. If that does not help reinstall the old thermostat or another thermostat. If the problem persists after that then you need to call a pro.
My thermostat dies every three days after changing batteries. If heat is “on” when it dies the heat runs and runs and runs. Woke up and it was 94 degrees. Can tell it is dying because the #s begin to fade.
time to replace it………..
I had to turn off the breaker to the circuit that powers the heat unit. Now the thermostat does not turn on. It is an LX model.
My themostat is set on 72 heat and is saying it is 74 indoors while it is 60 outside. The heat is not on and it has been in the same place for some time without any problem. Can there be a fixable problem without having to call HVAC? (nothing major).
replace it if you can if not then you will have to call a pro…..
I have a 10 yr old Honeywell non-programable Digital T-Stat that has been working just fine.
Returned from holiday vacation and it stays 3 degrees different between the set temp and the actual shown temp. i.e. I set it on 70 degrees, it runs until 67 degrees. This is pretty constant whether adjusting up or down.
Is this simply a bad thermostat?
Not sure. Some thermostats need to be calibrated and also make sure it is level. I would rather suspect something might be going on with your heating system rather than the the thermostat (from my experience) but it is possible something is going on with the thermostat. To be certain call an HVAC company to come out and check everything out to make sure it is working normally including the thermostat. I would let them do their check and then mention the issue with the stat.
I have a Honeywell focus pro 5000 non programmable thermostat. No matter where it is set. Right now at 69 degrees. It will not get above 63 or 64 degrees. Furnace running constantly but only putting out minimal heat. Is it the thermostat or could it be the furnace. If it is the thermostat, is there anything I can do to fix or do I need to call repairman?
It sounds like a furnace problem. Of course much of that has to do with the insulation in your house including doors and windows. A good tight house will retain the heat much better than one that is not. It is the basis for the heat loss calculation to size the heating system properly.
I have a Programmable Thermidistat Control. The indicator does not show anything and the Air Handler still works with cool air flowing out from vent. What is the problem?
I have a programmable digital Honeywell thermostat that is about 10 years old. I just turned the heat on for the winter. It is set at 58 overnight. I woke up to hear the furnace running. The thermostat says the indoor temperature is 68. Why is the furnace running?
Not sure about that Dianne without looking at it first. You likely need to call a service company to look at it. Perhaps the thermostat has gone bad.
honeywell th3110d t-stat non-programable, gas forced air. Unit 4 yrs old. began to not starting when the room temp falls below the set temp on occasion. Sometimes had to turn off and on to get running or if that did not work, turn set temp below room temp and turn off, then turn on and raise set temp to desired level and sometimes repeat. Furnace limit switch and flame detector okay. With furnace failing to run when it should be, shorted red and white wires of T-stat and instantly it began to operate raising temp to set level. Other times system operates normally for several hours. But at least once in 24 hrs I have the problem of furnace not turning on and temp drops to 55 deg F.
Off the top I would say change the thermostat. If it works fine when you jump between R and W then I would say its the stat but really can’t say without looking at it myself.
I have a central air conditioner/heater on my roof. I am having trouble with the heater. I turn the heater on and it clicks but doesn’t ever turn on. I tried the fan and ac and both of them work good but the heater wont blow out. Is one of the sensors out in the thermostat?
No, you likely have something wrong with the heating system itself and it needs to be looked at by a pro.
Had installed a dual fuel (propane) system 4 ton replacing a 2.5 ton system in 2017. 2017 was a mild winter, but 2018 has already broken records. I set the thermostat at 69 and most times it works fine. However, on these cold mornings when I wake up it is 65 deg. and nothing is running. I can then switch it off and back on and it will start up. (one time when I turned it off and back on I watched it immediately, within a second, go from 65 as the temperature to 69).
The tech has replaced the thermostat with another just like it and at one inspection noticed that the intitial two tubes fired up, but then the main tubes did not kick in (I don’t know what else to call them but tubes). Sometimes it did, sometimes it didn’t. His only thought left is that maybe since I upgraded 1.5 tons that the line from propane tank into the new system needs to be bigger and he is coming Friday to put that in. The air conditioner works fine, so I assume the problem must be in the main unit somewhere. Any ideas or suggestion would be much appreciated.
Actually, whoever installed the new furnace should have done a calculation on the size of the gas piping for the supply. This is basic-basic stuff and should have also been included in the startup of the furnace for manifold pressure and pressure drop across the gas valve. Pressures are adjusted at regulators and gas valves to make sure it meets specs. Those are all tests that are performed when a new furnace is started for the first time. There are other tests but for your problem, as you describe this should have already been done before the green light was given for safe furnace operation.
One other thing, most gas furnaces including new valves come setup from the factory for natural gas. If you have propane the gas valve needs to be converted for propane. There is a small kit that comes with all gas valves to convert them for use with propane. Propane and natural gas are different gases and operate at different pressures. Additionally, the spuds in the manifold need to be changed for use with propane. This can void the warranty if not done and it can also cause problems with the heat exchanger including a failure of the heat exchanger.
Little details like this are why I never recommend homeowners or even DIYers install their own furnaces. It can result in a dangerous situation that causes someone to become sick or even worse. Please make sure this is done properly not only for your comfort but also for your safety.
The system was installed by a licensed technician. I know he converted to propane because I was there when he did that. I will point your comments out to him when he comes Friday. He has been in business for over 30 years. It is just a mystery that he and others in the field can’t figure out. I was going to buy a new thermostat, but your comments leave me to believe that has nothing to do with this problem. Fingers crossed that the new piping will fix it. Thank you for your suggestions.
Hello in my apartment I set my heat to 74, stage1 pops up when it drops to 73 but don’t come on till it drops to 70 and stage1 and stage2 pops up. It just does this for the heat but not for the a/c. The a/c comes on 2 degrees from what I set it on. What can I do? Thank you in advance!!!
The answer is not so simple without more information and knowing what type of thermostat you have. I suspect the problem is in the settings of the thermostat and depending on the thermostat will depend on how you get to the basic setup settings for the system. Here is an article that may help you with the problem for two-stage system thermostat problems. The problem could also be something wrong with the heating system itself.
I just had a Ruud 802V Furnace and RA14 AC installed along with the Ruud Econet thermostat with Wifi.
I am having problems with the furnace running too long, causing calls for 1 degree in temp to end with about a 4-degree overall increase by the time the furnace finally shuts off.
This happens both in manual and “schedule” mode. It appears to me that the thermostat is “sluggish” in that it does not sense a temp increase until many minutes after the temp has actually increased.
I have compared the temp with another digital thermometer which makes it obvious that this is occurring. The thermostat temp display will continue to increase after the furnace turns off and eventually after 30 or more minutes will show the correct temp, but by then the house is 3 degrees hotter than it should be. I am having trouble convincing the HVAC install company that there is something wrong with the thermostat. I have even taken photos with the thermostat and the digital thermometer side by side showing the discrepancies. They are still not convinced.
I am curious as to your opinion.
Not certain about Ruud communicating thermostats but there should be an installation setting for temperature settings. Sounds to me like something isn’t quite right in the installation setup of the thermostat if it has one. There are also features in advanced thermostats that take some time for the program to get right. Things such as optimal start is a part of the program that will start the system ~30 minutes to ~1 hour to give the system enough time to make the house comfortable according to your desires and the capability of the equipment. In an older thermostat, I would say you have an anticipator problem that needs to be adjusted but the newer thermostats automatically adjust themselves.
I have a Braeburn brand thermostat.
I just bought this house recently, and i believe it was vacant for a couple of months so probably the HVAC/Furnace isn’t in operation for quite some time.
The 1st day i got it, i tested the AC and it works but i did not test the HEAT.
And 4 weeks later which is yesterday, it started to flash low battery so i replaced it with new batteries.
I test the unit by flipping to COOL and HEAT, both occasion i heard the “CLICK” sound and the display show fan is on, but nothing blows out neither the AC or the HEAT. I did a few trial and error, and ended up removed the batteries, and hit the reset button and left the thermostat detach from the wall for a few hours.
Put it back on, and surprisingly the AC works now.
However for HEAT, i try to change the temperature but for whatever reason, the temperature control DOES NOT let me go pass 45f.
For COOL, it works fine i can change the temp up and down. But heat, it just stay at 45f no matter how i press the UP and DOWN button.
Any idea or help you can provide?
Time to replace the thermostat……………from what you are describing
I have a trane thermostat. The display is blank. No light or anything but it has power to it. 27 volts according to my Fluke meter. There is not a battery in it so its getting power from unit. The air will not come on because the thermostat is not working. Is thermostat bad.
Yes, time for a new tstat.
I set my stat on 73 degrees for cooling and the unit work fine,However it will turn off and a minute later cut back on tripping the circuit breaker. I did a ohm check and ground check on the compressor and it was ok. I replace the capacitor and contactor. Do I need a new thermostat.
Likely not the thermostat. Something else is bad with either a motor or bad wiring. Best to call an HVAC tech.
I have 2 Carrier digital tstats in my house. I the one for the 2nd floor may need to be replaced. The display is sometimes is not clear. Also today I opened the door to adjust the temp and the whole thing went blank and the AC shut off.
I would check the wiring first and then if you do not find any issues there then replace it.
Hi. I live in a mixed use building. the thermostat is right outside my door in the hall. The settings are all set to 70 and the temp rarely reads above 59 in the winter and so heat should be on all the time. However it goes off at night and comes on sometime the next afternoon. could someone be turning the tripper off? the thermostat itself always looks on and always reads ‘on’.
There are some fake thermostats or some thermostats set up by building maintenance to read what you are reading on the thermostat. It often times reduces complaints although wiser people catch on pretty quickly.
I have a Carrier thermostat that recently has started to oscillate between off, cool and heat, seemingly randomly. We set the temps for cooling and heating, time, day, and all of those programmed pieces of data remain, but the t-stat just randomly switches between heat, cool and off (doesn’t ever go blank, it just displays “off”).
The switching between each setting might happen every second, or there might be a minute or so between the setting changes.
Wondering where I should begin looking to diagnose the problem.
Thanks in advance!
Jeff, I started to reply to this and it got a little lengthy so I turned it into an article. See Carrier Thermostat Intermittent Problem
I have a Rheem Thermostat and A/C. The past week the thermostat occasionally shows Power Fail and the a/c does not kick on to cool. It will eventually kick on and cool but not reach the preset temp. This only happens during afternoon hrs when it is the hottest outside, it runs perfectly overnight and during the morning hours.
Not 100% sure but with your description of the problem I would say it could be the thermostat. There really is no reason for the transformer to stop feeding power to the thermostat unless someone is turning the power off for the air handler. That could happen unintentionally sometimes but probably it is unlikely in your case. Sounds like something is getting hot and failing. Like an electronic component inside the thermostat. Recheck the wiring behind the thermostat to make sure it is good. If none of that works then try a new thermostat. One other thing:
Has anyone done any work in the house that involved putting a nail or screw in the wall? Possibly nicked the thermostat wire and when it gets hot the 24 volt hot wire or common separates and causes a power loss to the thermostat?
I have a 4 year old Lennox a/c and furnace. The Lennox ComfortSense 5000 series thermostat backlight came on during the night and woke us up. It is a very bright green color. I checked the panel on the thermostat and nothing was flashing, i.e., low battery, etc. It stayed on for about 10 minutes and then went off. It turned on 2 more times overnight for the same amount of time. This has never happened before. It has a battery back up and we checked the circuit breaker. Everything was fine. What could be the problem? I was hoping it was something simple and won’t need to pay an HVAC person to make a service call.
I can’t be certain about that type of thermostat. Probably best to call Lennox.
I have a rheem thermostat tst401mdms thermostat that works great except for one issue. I cannot reset the time. We had a power outage and I went into the menu, then hit the time button but nothing happens. Every other button work properly and other wise it works great. Is there some trick to setting the time?
I not aware of any type of reset on that thermostat. You will likely need to consult with Rheem. I sincerely hope it is still under warranty because I suspect it could be bad.