Table of Contents
- One of the most common trouble calls for HVAC heating and cooling
- Basic checks of the HVAC System thermostat to see if it is broken or?
- The basics of the thermostat for an HVAC system
- Learn what a heating anticipator is and what type of thermostat uses them.
- Fixing a Broken Thermostat for an HVAC System
- Finally, lots of related useful links to help you learn your heating and cooling 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. While the thermostat may be the problem, make sure you eliminate other possible heating and cooling problems.
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.
Troubleshooting Broken Thermostats
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. The thermostat may be the problem but first, make sure to double-check the simple things first. Therefore, a little thermostat troubleshooting is in order.
Common Trouble Signs | Troubleshooting Broken Thermostats
There is a possible quick fix to the broken thermostat.
- Check the power circuit at the circuit breaker and the HVAC equipment.
- If the thermostat is battery-powered try replacing the batteries on the thermostat.
- Make sure to double-check the components and settings in the program for a digital thermostat.
- Check for drafts and other location problems.
What To Check - Detailed Checklist | Troubleshooting Broken Thermostats
- 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 | Troubleshooting Broken Thermostats
- 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 backlight 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 | Troubleshooting Broken Thermostats
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 backlight to function on the thermostat.
Types of Digital Thermostats for HVAC Systems | Troubleshooting Broken Thermostats
There are two main types of digital thermostats; Digital thermostats that use batteries for the backlight 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.
Thermostat Troubleshooting 101 | Troubleshooting Broken Thermostats
- The thermostat may have Power Problems - Check the Power
- Location
- Drafts
- HVAC System Anticipators
- Mechanical Thermostats for HVAC Systems
The Program is Gone | Troubleshooting Broken Thermostats
Fixing a Broken Thermostat - Check the Power
The programmable thermostat is always losing its program. Is it a broken thermostat or simply a malfunctioning thermostat? This is most likely one of the older thermostats that use the power from the HVAC system. Additionally, every time you lose power you lose the program inside the thermostat. The thermostat may have power problems or it could be coming from the HVAC system. Furthermore, programming a programmable thermostat may 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 thermostat with one that uses power stealing technology. This should solve the problem. This type uses power from your HVAC system to hold the programs. Additionally, it has a battery backup just in case you lose power to your HVAC system. Lastly, this can save you lots of trouble and frustration and solve the problem. 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 | Troubleshooting Broken Thermostats
Location and Room Temperature
Is the heating and cooling thermostat installed in the proper location? You want the thermostat to read the natural room temperature. 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. You want the thermostat to sense room temperature and not be influenced by direct sunlight or other heat sources.
Additionally, thermostats installed where direct sunlight can hit the thermostat are going to be a problem also. This will give you false readings and cause your heating and cooling HVAC system to run erratically. 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 that produce heat, etc… will never offer accurate temperatures and conditioning for the room(s). If the thermostat is affected by other heat sources other than room temperature, it will appear as a broken thermostat or malfunctioning thermostat.
Drafts | Troubleshooting Broken Thermostats
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 and your HVAC system should maintain proper room temperature.
Remove the thermostat cover and make sure to check the hole in the subbase. This is where the wires come from the wall and are only seen when the cover is removed from the subbase. This can cause your heating and cooling system to cycle unnecessarily because the draft is causing an invalid temperature reading. Make sure to remove the cover and check for this problem. Lastly, make sure the hole is insulated to prevent drafts from affecting the temperature reading on the thermostat. When finished, make sure to replace the cover and test.
Anticipators | Troubleshooting Broken Thermostats
Has the heating anticipator been properly set by a qualified air conditioning and heating technician? It is for the heating system operation. The heat anticipator is on mechanical non-digital thermostats. Additionally, it needs to be set according to the amp draw on the heating system 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. When this is not set properly, your heating system will not cycle properly. Therefore, make sure your heating system anticipator is set to the proper setting.
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 for the heating system. 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 | Troubleshooting Broken Thermostats
Fixing a Broken Thermostat
The thermostat may not be level. 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. A level thermostat will solve the problem of an inaccurate thermostat.
Additionally, if the thermostat components are dirty you can use a slight amount of compressed air or a small soft brush to gently clean the dirty components inside the thermostat. As a technician, I often carry a can of the computer cleaning compressed air and a small soft brush.
I gently clean the inside components and check the other things noted above. It is important to use a soft brush or compressed air for this as you do not want to damage any of the components. Using a soft brush or compressed air to clean the components will solve the problem of any dirt causing the issue.
Other problems that can occur with your air conditioning and heating thermostat include power surges that can cause a malfunctioning thermostat or broken thermostat. Those other problems need to be discussed with an Heating and Cooling HVAC professional. Furthermore, these problems can be technical, require professional thermost troubleshooting, and require special tools to fix. They can solve the problem with a broken thermostat quickly and efficiently. It is always a wise choice to call in an Heating and Cooling HVAC professional when you have problems with your air conditioning and heating equipment, Lastly, that includes thermostat troubleshooting for your air conditioning and heating thermostat.
Troubleshooting Broken Thermostats
Heating and Cooling - Troubleshooting Broken Thermostats
Heating and Cooling Thermostats Color Codes video for basic thermostat troubleshooting and replacement.
COVID 19 Home Protection
UVC Light to Kill Viruses and Other Airborne Harmful Things that Affect Health
For additional protection, you can also use UV Light that will kill harmful viruses and bacteria inside the airflow of the air handler. In labs, researchers used a spectrum of ultraviolet light called UVC to kill viruses. This product requires professional installation so it will turn on and off with the blower fan in your air handler but it will offer the protection you need for you and your family from any viruses.
Click the image to the right for purchase options of the UV light to protect your family.
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.
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.
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.
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 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?
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.
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.
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.
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 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 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.
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.
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.
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.
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.
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.
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.
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 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.
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.