5 Reasons Your Thermostat Isn’t Working

Thermostat on wall
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You could say that the thermostat is the brain of your HVAC system. As the brain, it does the important job of communicating your home's heating and cooling needs to your HVAC system. Once it reads the needs of the home, its components tell the HVAC system what to do, while continuously monitoring the home's environment and giving the system further instruction.

When things inside a thermostat go awry, your HVAC system as a whole can take a turn for the worse. However, pinpointing exactly what is causing your thermostat issues can sometimes be difficult. Here are a few common reasons thermostats fail and how you can remedy them.

The Thermostat's Power Source Is Failing

You head over to your thermostat and notice the screen is dark. More than likely, this means there's no power getting to it. First, ensure the power switch is fully engaged. If so, remove the cover and replace the battery. If this doesn't do the trick, look for a blown fuse or tripped breaker.

The Thermostat's Connections Are Loose

Your thermostat relies on a few essential electrical connections to get the job done. When a thermostat senses a problem, each individual connection allows it to send power to the necessary component for the solution. Most basic thermostats include a heating connection, cooling connection, and fan connection. When these connections are compromised due to loose wires, corrosion, or any other reason, your thermostat will be unable to properly communicate with your HVAC system.

Troubleshooting Faulty Thermostat Connections

Before troubleshooting anything electrical, always start by turning off the power at the breaker. Before getting too far into this process, make sure there are no obvious signs of compromised connections. Use a screwdriver to tighten each terminal and, if you suspect corrosion, pull each wire out of the terminal and inspect it. Should a wire be corroded, use wire strippers to remove the corroded section and reveal a new section of wire before reinstalling in the terminal.


Working around electrical components can pose a significant safety risk and should only be done by individuals who are both knowledgeable about the process and confident in their abilities to safely perform the task. If you aren't comfortable testing your thermostat's electrical connections, consult with a professional to safely get the job done.

If your thermostat still isn't functioning properly, you will need to manually test the connections. To do this, use a wire nut to attach the red power supply wire to the green fan wire, then turn on the power. If the fan comes on, this is a sign that your thermostat is failing to send the signal to the fan. If needed, repeat this process with each connection.

The Thermostat Is Dirty

Thermostats, like many other electrical appliances, will malfunction if they're allowed to get too dirty. Dirt, dust, and debris can pose problems for both electrical and mechanical components, causing your thermostat to fail. Turn off the power source and remove the thermostat's cover. Using compressed air or a small brush, clear the housing of any dust and debris. Once finished, replace the cover and flip the power back on.

The Thermostat Isn't Level

Does your thermostat's temperature readout not match the room's actual temperature? This could be because the thermostat itself isn't level on the wall. Thermostats that feature a mercury bulb must be level to operate. To fix this, turn off the power supply and unmount the thermostat. Use a level to ensure it's perfectly level when remounting.

The Thermostat Is Installed in the Wrong Spot

Maybe your thermostat is properly communicating with your HVAC system, it just never seems to keep up with your home's needs. A thermostat installed in an improper place in your home can sense an inaccurate picture of your home's environmental needs.

For instance, a thermostat positioned directly above or beneath a register will prematurely shut off, as it senses the home is at the proper temperature before the entire home is cooled or heated through. To remedy this, the thermostat will need to be moved to a central area of the home, away from registers, windows, and doors.

When to Replace Your Thermostat

There are two main reasons you would need a different thermostat. First, your thermostat could simply be in need of replacement because of age. Like most components of a home, thermostats eventually get old and go bad.

Secondly, your thermostat could be improperly paired with your HVAC system. Just like there are many different thermostats on the market, there are an assortment of different HVAC systems. It's important to have a thermostat that works with your system and is capable of telling your specific HVAC unit how to operate. To ensure you have the correct thermostat, compare your HVAC system's requirements with your thermostat's capabilities. If replacing, be sure you buy a thermostat that will work with your system.

When to Call a Professional

If you've tried these simple troubleshooting tips to no avail, it may be time to call in a professional. From electrical knowledge to in-depth knowledge of different HVAC systems, an experienced HVAC technician will have all the tools and know-how needed to get your thermostat up and running without a hitch, no matter the problem.