What you will learn from Troubleshooting Broken Thermostats article:

  1. One of the most common trouble calls for HVAC
  2. Basic checks of the thermostat to see if it is broken or?
  3. The basics of the thermostat
  4. Learn what a heating anticipator is and what type of thermostat uses them.
  5. Fixing a Broken Thermostat
  6. 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.

Related Link: How to Hook up a New Thermostat - A Closer Look

Troubleshooting Broken Thermostats

What To Check

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
  • 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

  • tstat repairThe 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.

  1. Power Problems
  2. Location
  3. Drafts
  4. Anticipators
  5. 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.

Related Link: How a Programmable Thermostat Works - A Closer Look

If the problem is persistent with the thermostat it is important to get back to thermostat basics.

Fixing Broken Thermostats - The Basics


Fix Broken ThermostatIs 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).


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.


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.

Related Link: Learn more about thermostat types - A Closer Look

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

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Troubleshooting Broken Thermostats

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