How To Test A Home Thermostat

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Are you having trouble with your heating or air conditioning, Is the temperature inside your home too hot or too cold? In this post I will tell you how to test a home thermostat and help you decide if it might be time to replace your thermostat.

By the end of this article, you will know how to test your thermostat and bypass it if necessary to get your equipment working again.

If you are having problems with the heating or cooling system in your home your HVAC system may not be the problem it might just be a malfunctioning thermostat.

At the end of this article, we’ll also provide some tips on choosing the right replacement thermostat for your needs.

Step 1: Look at your thermostat

If the heating and cooling system in your house is not working and you think it may be a faulty thermostat, the first thing to do is check that it is turned on and set to heat or cool your home. If it is a digital thermostat look at the screen and make sure the display is on and set to heat or cool your home to your desired temperature. Check the programmed settings and make sure they are correct.

Step 2: Check the batteries.


Batteries, check for any low battery or blinking battery light or indicator. Doing a battery change is an easy way to rule out a low battery as the problem. If your thermostat display is blank and changing the battery does not fix it, or it does not have a battery you might have a wiring problem, a bad thermostat, or an issue with your HVAC power supply. You can read my article on batteries here

Step 3: Check your breaker box

Check your breaker panel and look for your HVAC breaker, it could be marked heater, furnace, or air conditioner. Make sure it is turned on and not tripped. If it was off and or tripped turn it on and see if this fixes your problem. If it was tripped and trips again you should call an HVAC professional as there could be something wrong with your system or wires.

Step 4: The simple test.

First, turn your thermostat to its off position, and wait for 15 minutes. Then turn your thermostat to the heat setting and turn the temperature up to a setting that is warmer than the room’s temperature. On some thermostats, there is a delay and you may be able to hear a click once it signals your furnace to turn on. Once you have done this check and see if your heater has turned on and the furnace burner has lit. If you are unsure if the burner is lit, you can wait to see if hot air comes out of the vents or if you have radiators if they start to warm. If your blower starts running but the burner in your heater does not light you could have problems with your heater and not your thermostat. I will tell you how to check this later in this article.

If you are testing to see if your air conditioning system works, you can do the same test just turn your thermostat to the cool setting and see if the fan comes on and if the compressor starts on your outdoor unit, again some thermostats have a delay built in. If the fan comes on but the outdoor unit does not turn on you may have a problem with the air conditioning system and not your home’s thermostat. If you are not sure if the system has turned on you can wait and see if it starts blowing cold air.

Step 5: Check wires


For this step, you need to first turn off your furnace or air conditioner. Look for a switch to turn it off, if you can’t find a switch go to your breaker box and look for the breaker it should be labeled “HVAC” or “furnace” or “air conditioner.”

Once you have the power turned off, go to your thermostat and Remove the front of the thermostat. Most thermostats either have a cover that comes off or the entire body comes off, pull from the front to remove the cover or the body. Take your time so you don’t damage the thermostat. You should be able to see the wires inside coming from the wall into the thermostat.

Check that all the wires are in good condition, and not broken or disconnected. Make sure the connections at the terminals are tight.

Once you have done this, replace the front of your thermostat and turn the power back on. Check to see if this fixed your problem.

Step 6: the bypass test

  1. To turn off your HVAC system, find the on/off switch and flip it to the “off” position. If there is no on/off switch, go to your home’s breaker box and switch off the circuit labeled “HVAC” or “furnace” or “air conditioner.”

  2. Remove the thermostat cover. Most thermostats pull off from the front or have a cover that comes off. Take your time so you don’t damage the thermostat. You should be able to see the wires coming from the wall into the thermostat.

  3. For this step I recommend taking a picture or writing down what color wires go to what terminals before proceeding. Once you have done that, look for the wire connected to the R terminal or Rh terminal If you are testing for heat, or the R or Rc terminal if you are testing for air conditioning. You need to remove this wire from its terminal this wire is usually red. Next find the wire connected to W or the white wire for heat, or the Y or yellow wire for Cooling. If you are testing heat twist the R or Rh wire and the W wire together. If you are testing cooling or Air conditioning, twist the R or Rc wire together with the Y wire. Once you have done this, turn your HVAC switch or breaker back on. If your system turns on and starts making heat or cool air then your thermostat needs to be replaced.


Your HVAC system is controlled by your thermostat. The thermostat setting is compared to the thermostat’s reading of the room temperature. This controls the heating or cooling in your home. If your thermostat is taking inaccurate temperature readings or is not functioning at all your HVAC system will not work to keep you comfortable. The tests I have outlined in this article should help you determine if the thermostat is the problem or if you have faulty furnace wires or cooling system wires. You may also have other problems with your heat or air conditioning, in which case you should call your local HVAC professional for service and repair.

If you have determined you need to replace your thermostat, you can read my comparison and buying guide to help you select the right thermostat replacement here:

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