Home Improvement Skills & Specialties HVAC

7 Common Reasons Your Thermostat Isn't Working

How to Fix Thermostats and Keep Your HVAC Running Properly

Thermostat on wall
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Is your thermostat not working? Your thermostat is the brain of your HVAC system and it has 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. But things can go awry. While many HVAC problems seem at first serious, they're often just problems with a faulty thermostat and can be fixed with simple solutions. Here are a few common reasons thermostats fail and how you can remedy them.

The Thermostat's Power Source Is Failing

If the screen of your thermostat is dark, it more than likely means there's no power getting to it. First, ensure the power switch is fully engaged. If it is, then remove the cover and replace the battery. If this doesn't do the trick, look for a tripped breaker. Go to your main circuit breaker to see if there is an overloaded circuit that is flipped to the "off" position and flip it back to "on," which may fix the problem. You could also try flipping the thermostat cover open to see if there is a blown fuse inside the device that needs replacing.

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.

Warning

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, but it 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.

The Thermostat is Programmed Wrong

A smart or programmable thermostat may simply be adjusted because it is programmed to the wrong setting or heating or cooling at the wrong times. Sometimes you have to set a smart thermostat manually until it "learns" your preferences. Check your owner’s manual so you can learn how to access the device's features, such as temperature setpoints, timers, and schedulers.

The Furnace Switch Needs Repair

The thermostat may not be working if the furnace switch on your furnace isn't on. This switch has to be on to use the thermostat. If the furnace switch is off, simply switch it back to on. There could be an airflow or cycling issue that caused your furnace switch to turn off so you may want to consult your HVAC maintenance technician to check it out.

When to Replace Your Thermostat

There are two main reasons you would need to install a different thermostat. First, your thermostat could simply need 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 simple troubleshooting solutions to fix your thermostat but they did not work, it's time to call in a professional. Before calling, double-check that you tested the power switches and batteries, looked for faulty connections, confirmed proper installation, and cleaned the thermostat's housing. If these solutions fail to kickstart the device or the fixes do not hold, contact 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.

FAQ
  • Is there a reset button on a thermostat?

    Yes, most standard, programmable, and smart thermostats will have some sort of tiny reset button somewhere on the device. You may need to lift the thermostat's cover to find it. Press the button with the end of a paperclip for a few seconds and that should reset the device. Or, consult your owner's manual to find specific instructions for a reset button.

  • What happens when a thermostat goes bad?

    Your HVAC system will either stop working or work erratically. Rooms throughout your house may have very different temperatures, signaling a faulty thermostat. The display on your thermostat may stop functioning properly, as well.

  • How much does it cost to replace a thermostat?

    In general, it can cost an average of $200 just for labor, regardless of what type of unit you choose for a replacement. In addition to the cost of the unit, the price can vary due to requested add-on accessories or features, the number of units and zones that need to be serviced, and other complexities of the installation.

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  1. How Much Does Thermostat Installation Or Replacement Cost? HomeAdvisor.