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How Do I Test My Thermostat To Make Sure It Really Works?

However, a major part of this process is the regular maintenance of thermostats inside the home. 
Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Irrespective of whether it is winter or summer, a thermostat that is not functioning correctly can cause a lot of headaches, including low battery warning failure, inaccurate temperature readings, poor interior temperature control as well as lighting and energy efficiency issues. 

The good news is that there are ways in which you can test your thermostat to check if it’s functioning correctly.

So let’s take a look at some of these steps that you can take to properly inspect and maintain your home thermostat (see also ‘Best HomeKit Thermostats‘).

What equipment do I need to test my thermostat?

The only tool you’ll probably require to check your thermostat is a flat head screwdriver which will be used to remove the main plate of the thermostat so you are able to see inside.

How to test if the thermostat is properly installed?

If you’ve been experiencing inconsistent indoor air climate but higher energy bills, then it might be time to check the functionality of your home’s thermostat. She here’s what you can do to detect if your thermostat is functioning correctly or not.

Step 1  – Turn off HVAC power

This can be done by switching the furnace to the off position, or else you may need to cut the power off by locating your home’s breaker box and the circuit lever that’s labeled “furnace” or “HVAC.”

Step 2 – Remove the thermostat cover

Using a flat head screwdriver, remove the main cover so that you can see what’s going on inside. Depending on the model of thermostat you have, you may have to remove the entire body of the device. Ultimately, you need to have access to the wires inside.

Step 3 –  Remove wires from terminals

So once you get to the wires, they should be screwed to the terminals marked R, W, G, Y, and C, which stands for red, white, green, yellow, and common, respectively.

Thermostats only have two wires (see also ‘Thermostat Wire Colors Explained‘), which are either red and white or red and green. So make a note of these labels and snap a photo with your phone.

Thereafter, unscrew and remove the wires from the various terminals. However, ensure that they don’t fall back into the hole in the wall. You can wrap the wires on a pencil if you’re concerned about this. If there are more than two wires, then choose only red and white.

Then twist the bare ends of the two wires together and ensure that no other wires are making contact with them. 

Step 4 – Turn HVAC power back on

In this step, you’ll return power to the furnace or HVAC using the switch. If the blower turns on without the connection to the thermostat, then the unit or thermostat is defective and needs to be replaced.

Step 5 – Test other wires

Then switch the HVAC back off. Thereafter, twist R and Y wires together and turn the HVAC breaker back on. The fan should not be working.

Check to see if the air conditioning system ignites, then switch off the power again. If the HVAC passes all the above tests,  then the thermostat is faulty and needs to be replaced.

How to test if the thermostat is sending a signal?

Raise the thermostat heat settings gradually and slowly.

When you do this, both the thermostat and the furnace should emit a clicking sound. If it doesn’t do this, the thermostat is not sending a signal and needs to be replaced.

How to test if the thermostat is providing accurate information?

If you’d like to check whether your thermostat is providing accurate information, then here’s how you can go about doing it.

Start by taping a glass tube thermometer to the wall a few inches away from the thermostat. Pad the thermometer with a paper towel to prevent it from touching the wall.

You also need to ensure that neither the thermostat nor the thermometer is affected by outside temperature influences. 

In some cases, the hole in the wall behind the thermostat could be too large, thereby allowing cold air to reach the thermostat and affect its reading. 

You should then wait about 15 minutes for the Mercury to stabilize. Thereafter, compare the reading on the thermometer to the reading on the thermostat needle.

If the variation is more than a degree, check to see whether the thermostat is dirty.

In order to check for dirt, remove the faceplate, which is usually held in place by friction or snap switch. If there is visible dust or dirt, try and blow it away. Don’t use a vacuum cleaner because the suction is too great. 

If there are accessible contact points on the thermostat, rub a new dollar bill between them to clean the spots. Avoid using emery cloth or sandpaper. If the element is soiled, then use a soft brush to clean.

If the thermostat contains a mercury vial inside, make use of a level to ensure that the unit is straight. If it’s not straight, then loosen the mounting screws and adjust the thermostat until the mercury vial found inside is level. Thereafter tighten the screws.

Once a thermostat has been cleaned, check it again with the glass thermometer according to steps one and two, and if it’s still not calibrated, then it should be replaced.

Signs your thermostat is malfunctioning

Signs your thermostat is malfunctioning

Irrespective of what type of thermostat you have installed in your home, they all inevitably or ultimately malfunction due to natural wear and tear, certain defects or even lifespan. So here are some of the methods of determining if your thermostat is defective:

The display

If the display is missing data or the screen looks faded, then you can immediately tell that something is wrong. The culprit could be dead or dying batteries; however, your thermostat can experience missing or fading data for one or more reasons.

Incorrect temperature

If the building or room temperature doesn’t match the thermostat setting, then you could also have a thermostat problem.

A bad unit could be the cause of air conditioner temperature discrepancies. Additionally, if a thermostat was installed close to a hot or cold air source, it can also display the wrong temperature.

Strange behavior

An HVAC system that kicks on or off too much or too little when compared to maximum performance events in the past is another sign that you may have a malfunctioning thermostat.

Thermostat wiring

Any type of wiring problem such as corroded or loose wiring can cause a thermostat and, in fact, the entire system to malfunction.

Manual activation

If you cannot use the thermostat to turn the heat or air conditioning on and off and have to manually switch it on, then the thermostat is likely malfunctioning.


The thermostat not only regulates the temperature inside your home but plays a huge role in saving energy as well. Consequently, the greater the difference in temperature between the inside and outside of your house, the harder your thermostat has to work.

So the more efficient the thermostat setting, the more effective your system will work.

Consequently, the system experiences less strain, fewer repairs, and will also last longer, so in order to prolong the lifespan of your thermostat, ensure that you maintain it regularly and also keep an efficient thermostat setting, which will maximize the lifecycle of your system.

author avatar
Charlie Hardcastle


On Key

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