What you will learn from Troubleshooting Broken Thermostats article:

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

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

Troubleshooting Broken Thermostats

Common signs of a broken thermostat are: 1) Thermostat display is off or is blank. 2) The heat or AC is non-responsive to any settings on the thermostat.
There is a possible quick fix to the broken thermostat.
  1. Check the power circuit at the circuit breaker and the HVAC equipment.
  2. If the thermostat is battery-powered try replacing the batteries on the thermostat.
  3. Make sure to double-check the components and settings in the program for a digital thermostat.
  4. 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
  • 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

  • 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 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

  1. Thermostat may have Power Problems - Check the Power
  2. Location
  3. Drafts
  4. HVAC System Anticipators
  5. 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.

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

Location and Room Temperature

Fix Broken ThermostatIs 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.

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

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

High Performance HVAC

Heating and Cooling - Troubleshooting Broken Thermostats

Heating and Cooling Thermostats Color Codes video for basic thermostat troubleshooting and replacement.

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