Why Is My Thermostat Not Working?: 5 Things to Try When the Temperature Is Acting Up

There’s nothing nicer than returning to a cozy home on a cold winter’s night, but sometimes things go wrong with your system. If you’ve set your heating to turn on an hour before you're due back from work and you walk into a polar parlor, don’t panic. Here’s how to troubleshoot a thermostat that’s not working and find out if a simple and inexpensive DIY fix can keep things comfy.

Signs of Thermostat Trouble

Thermostats are pretty sophisticated devices, but they aren’t foolproof. Sometimes, you can easily recognize the signs you have a bad thermostat. Other times, you or a professional might need to investigate if another part of your HVAC system is malfunctioning. Common signs of a thermostat problem include:

• Blank thermostat screen

• Thermostat not switching on

• HVAC system not reaching programmed temperature

• HVAC system continuously running or not running a programmed cycle

• Not being able to change thermostat settings

• Thermostat continuously resetting

If you think your device isn’t working properly, it pays to learn how to troubleshoot a thermostat. Before calling out the professionals, try the following DIY strategies to get your HVAC system back on task.

1. Test Power

The first thing to do is check your thermostat has power. A blank screen could signify you need to replace the batteries. If the batteries lose power or suffer from corrosion, the screen might flicker or fade. Change the batteries in your thermostat and reset the device. 

Wired devices can be a little more troublesome. An unexpected power surge can trip the circuit breaker to which the thermostat is attached. Locate the associated breaker in your home’s electrical panel box and reset it by flipping it off and on again.

If the breaker continues to trip, there could be a bigger problem with your electrical wiring. At this stage, it’s best to seek help from a licensed electrician near you. You could have an overloaded or bad circuit breaker. 

2. Check Thermostat Settings

Sometimes, you might be stressing about the cost of replacing an HVAC system when all you need to do is learn how to read your thermostat properly and check the program settings. If your system is blowing out hot rather than cold air, someone could have accidentally flipped the mode from the AC to the heat setting. And if your heating switches at odd hours during the night, it could be on a manual 24-hour setting rather than your programmed auto mode.  

Always check your settings after a prolonged power outage, as they may reset to the manufacturing standard or manual mode.

3. Remove Dirt 

Include your thermostat in your spring cleaning checklist. A buildup of dirt can result in the device misreading temperatures because of sensor issues or compromised electrical parts. Here’s how to clean your thermostat:

1. Shut off the power at the circuit breaker or turn off a battery-operated device.

2. If the thermostat has a cover, flip it open (some modern, smart thermostats won’t have a cover).

3. Gently clean away dirt particles using a soft bristle brush or compressed air and a dry microfiber cloth. Never use a wet cloth around the delicate electrical parts.

4. Replace the cover and turn the power back on.

4. Change Thermostat Placement and Level

According to the U.S. Department of Energy, to operate properly, you should position your thermostat on an interior wall away from direct sunlight, drafts, doorways, skylights, and windows. Sticking it behind a big sideboard can also block air movement, and having it right next to a hot oven is a no-no.

If the fitter doesn’t install the thermostat well, this can also cause problems. A device that isn’t sitting level can produce inaccurate readings, especially if you have a mercury thermostat with this chemical sitting in a bulb.

If the location affects your thermostat's performance, you might need to move it. Sometimes, this will involve rerouting wiring, and you’ll need to hire an electrician.

5. Inspect Wiring and Connections

Loose or corroding wires can affect your thermostat’s performance and be a safety hazard. Here’s how to inspect the wiring:

1. Turn off the thermostat power at the circuit breaker box. Never remove the cover to expose electrical wiring without completing this step.

2. Consult the user manual for instructions for accessing and understanding the wiring for your thermostat model.

3. Remove the device cover and inspect the wiring for corrosion or loose connections.

4. If you see a problem, only remove the corroded section using a wire stripper, tighten loose screws, or connect detached wires if you are confident in handling electrical connections safely.

5. If you have any concerns, contact an electrician to repair the wiring rather than attempting to DIY.

Thermostat Maintenance Tips

No matter what model you opt for, thermostats won’t last forever. But you can take some simple steps to keep your thermostat thriving for as long as possible. 

• Replace batteries when they run low.

• Keep the device cover securely in place to prevent premature buildup of dirt.

• Clean dirt and debris buildup regularly.

• Avoid positioning in a room with high humidity. This can quickly result in corrosion of parts.

• Update software on smart thermostats.

• Reprogram if your HVAC system switches on and off more frequently than needed. The more your system has to work, the shorter its life span will be—and it can result in higher energy bills.

• Complete an annual HVAC inspection, which includes a thermostat check. The professionals can replace loose wiring or wonky sensors, remove corrosion, and advise on placement.

DIY vs. Hiring a Pro

Most of the tasks above are easy to DIY. However, if you’ve been through these troubleshooting steps and nothing is working or are concerned about wiring problems, call a professional thermostat repair service near you for an inspection. Your thermostat or something else in your HVAC system may need a tune-up or replacement parts.  

You don’t always need an electrician to replace a thermostat. If it is a battery-operated device or one that can hook up to your existing wiring, you could make savings by replacing the thermostat yourself. When you aren’t confident working with wiring, or it needs rerouting, call a professional—mucking up installation can cause blown fuses, tripped circuits, and performance issues.

The average cost to install a new thermostat is $180. The average HVAC repair cost is $350, but repairs to the thermostat, like replacing the sensor, will be significantly less.