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.
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.
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
- 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 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
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 for HVAC Systems
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.
Thermostat Troubleshooting 101 - Broken Thermostat
- Thermostat may have Power Problems - Check the Power
- Location
- Drafts
- HVAC System Anticipators
- Mechanical Thermostats for HVAC Systems
The Program is Gone
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 back-up 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
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 is 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
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
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
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 a 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.
We have a Lennox system. The set point for AC is 74 and it continues past that point and has been constantly blowing cold air – the room temp has been between 63 and 67. I have reset it and powered off and on the system. It seemed to stay at the set point yesterday but went past it last night and is currently at 65 with cold air blowing.
I recommend calling for service from a Lennox dealer.
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.
Hello there, High Performance HVAC, I have a 2006 Carrier Air handler, that keeps tripping the breaker, and the thermostat is turned off, it trips the minute you reset it, any ideas?
Likely you have a dead short or a bad breaker. Best to call for service. You can also get more info in this article about breaker trips.
We have a american standard 7day digital programable thermostat that is 20 years old and an american standard heat pump and it kept short cycling 6weeks aho so air conditioning refrigeration tech replaced motor on heat pump and capacitor and worked great 1week and had to call him out again and he then said he will replace thermastat batteries and lithium battery on therastat and it worked 1week and now he says we need thermastat replaced but my husband and I have no heat so we googled how to do a reset on thermastat and we did that tonight and it came on the heat pump but only for about 15min ifvthat and it stopped so fo you think we need new 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 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 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
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 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.
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.
The light on my thermostat is no longer bright and it is hard to read the pane. I changed the batteries but the panel on the thermostat is very dim. Sometimes I think I’m on air but I really have turned on the heat. It is working fine. House cool and comfortable …just can’t read the thermostat
Some thermostats have a way to increase the brightness on the display. You’ll have to get the instructions to see if your thermostat has this feature. If not, then likely the display is going out and the thermostat needs to be replaced.
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 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 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.
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.