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.
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UVC Light to Kill Viruses and Other Airborne Harmful Things that Affect Health
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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.
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.
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 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.
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 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 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.
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 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 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………..
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.
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.
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.
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 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 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.
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 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.
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 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.