How to Check if Your Thermostat is Sending a SignalKnowing how to check your thermostat when your HVAC system won’t turn on might get your system running again quickly without having to rely on a pro. Since thermostats control when furnaces and air conditioners turn on and off, troubleshooting this device can rule out whether your equipment needs deeper testing for a thorough diagnosis.

Many programmable thermostats contain batteries that deplete their charge after a year. Open the cover of your device, remove the batteries and replace them with a fresh set. Your HVAC system should turn on shortly after you replace the batteries. If your system still won’t run, you may need to call in an expert.

Some thermostats are hard-wired into the home. To test them, switch your thermostat “off,” and then switch back to “on.” Set it to the heating or cooling mode, and turn it up or down, depending on the season. Some thermostats will make a clicking sound when they turn on — you might even hear your HVAC system click on as well.

If you have a gas furnace, you might hear the gas ignite. If the distance between either is noticeably far, enlist a family member to stand by the air handler and signal to you when it should make a noise and start running.

You can test your thermostat further if you have a gas furnace by turning off the circuit breaker that controls the furnace and air conditioner. Snap a picture with your camera or phone for later reference. Then, unscrew the wires labeled R, Rh and W. Once loose, twist all three together and turn the circuit breaker back on. Regardless of season, if your furnace starts up, this indicates that the problem lies with the thermostatic control and not your heating or cooling system.

Before tossing any thermostats in the trash, verify that they don’t contain any mercury. If they do, take it to your nearest hazardous waste disposal agency.

The pros at Around the Clock Air Conditioning & Heating can diagnose and replace a malfunctioning thermostat in your home. We’ve provided trusted HVAC services for Los Angeles homeowners since 1967.

Our goal is to help educate our customers in Los Angeles, North Hollywood and surrounding areas about energy and home comfort issues (specific to HVAC systems). For more information about thermostats and other HVAC topics, download our free Home Comfort Resource guide.

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