7 Reasons Your Thermostat Is Acting Wonky

Amy Pawlukiewicz
Written by Amy Pawlukiewicz
Updated December 15, 2021
Man choosing temperature on thermostat
Photo: rh2010 / Adobe Stock


  • The cost of a thermostat replacement averages $175.

  • Fixes might be as simple as replacing the batteries or cleaning the thermostat. 

  • If you need wiring work or a new unit, call a pro.

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Whether your home has an older HVAC system with an analog dial or a smart thermostat you can control on your phone from the comfort of the couch, problems can still arise. For example, your thermostat is set to cool on a hot summer day, but the heater kicks on—or vice versa. Here’s a breakdown of why your thermostat might be acting up (and what you can do about it).

How to Troubleshoot a Thermostat 

Here are some steps to take if your thermostat has gone haywire.

1. The Batteries Are Bad

If the thermostat’s batteries are worn out, running low on power, or corroding, they can cause your thermostat to act up. Low batteries are the most common (and easiest) issue to fix, so start there.


The first thing to do if your thermostat is acting weird is to change out the batteries and see if that fixes the problem. If you see corrosion, don’t touch the battery with your bare skin, and make sure moisture isn’t somehow getting into the thermostat.

2. The Thermostat Is in the Wrong Spot

Round smart thermostat with touch screen
Photo: rh2010 / Adobe Stock

To properly sense temperature, the optimal location for your thermostat is five feet above the floor in an open area. If your thermostat is placed in a corner, near a vent or windows, or in a closet, it will read the temp of that area’s unique microclimate versus how it feels throughout the rest of your home.


You’ll need to move your thermostat to an open area where it can get an accurate reading. This involves rerouting wiring, so hire a professional electrician near you.

3. There’s Dust in the Mechanism

Dirt and dust builds up on your thermostat over the years and can cause it to misread the temperature. Luckily, it’s easy to clean. 


Shut off the power to your thermostat at the fuse box. Remove the cover from the thermostat, and clean the inside with a soft brush. Use a smaller brush to get into the nooks and crannies where dust and dirt might be hiding.

4. Your Thermostat is Reading the Wrong Temperature

Your thermostat may be registering the wrong temperature. For example, it’s a hot day and it’s 82 degrees out, but your thermostat jumps to 74 degrees. The air conditioner or heat won’t kick on because the thermostat is reading the wrong temperature in the room.


Grab a working thermometer and hold it next to your thermostat. If the readings don’t match, then your thermostat is incorrectly reading the room temperature. This is a common problem with older thermostats that rely on mercury bulbs. Consider switching out your thermostat with a newer digital model.

5. The Wiring Is Loose

If you notice that your HVAC system isn’t keeping your home at the desired temperature, your thermostat may not be connected properly due to loose or corroded wiring. 


Start by turning off the power to your system at the fuse box to prevent damaging it or injuring yourself. Remove the cover, and make sure all of the wiring connections are secure. Consult your manual if you are unsure of how to check the wiring.

6. The Thermostat Is Old

Unfortunately, mechanical appliances don’t last forever, no matter how much we wish they could. If you have an older thermostat, it may be failing simply because of its age.


It might be a good time to upgrade to a digital thermostat. The average cost to install a new thermostat is $175, and there are lots of options on the market. Smart thermostats tap into your Wi-Fi, so you can automatically turn the heat down when you’re at work or turn it up on the weekends when you’re at home snuggling with a book. Some allow you to program a schedule and learn your usage patterns, so you can save on energy. 

7. There’s a Mechanical Issue

Sometimes it looks like the thermostat’s malfunctioning, but the problem is actually with the HVAC system itself. Frozen AC coils, poor air circulation, and dirty sensors can all cause your system to run improperly.


If you’ve been through the troubleshooting steps above and nothing is working, call an HVAC technician near you for an inspection. Your system may need a tune-up or replacement parts. This is a job best left to the pros, so you don’t damage your system. Once it’s up and running again, you can look forward to comfortable temperatures and not having to fight with the thermostat.

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