Why Is My Thermostat Blinking?

Why Is My Thermostat Blinking?

If you’re like most people, any time lights start blinking around you, you’re going to be a bit alarmed. It’s one thing when those lights are something you’re familiar with, such as your alarm clock or car hazard lights, but it’s another when it’s something unfamiliar, like anything that’s a part of your HVAC system.

So if you’re thermostat is blinking, here’s why.

Problem with the Battery

One common reason why your thermostat may be blinking is that it has a low battery and it is warning you it's time to replace it before the battery dies.


Changing your thermostat's battery is quite simple. You just have to unscrew it from the wall, replace the batteries, and screw it back on. However, if it continues to blink after you've changed out the battery, there may be a bigger problem with your thermostat.

Problem with the Outdoor Unit

If you see a flashing light on your thermostat, that's a signal that there’s a problem with your outdoor unit. When this happens, your outdoor unit will shut off and send a signal to your thermostat, causing it to blink. Thing is, that signal doesn’t mean your indoor unit is made aware of the problem. Your indoor unit will probably continue running and the thermostat will keep blinking until the problem is fixed.


Most often, you’ll need to shut off your indoor unit for a minute, then turn it back on after 30 seconds, causing the light to turn off as well. Wait about 10 minutes, then check to see if your outdoor unit has turned back on.

  • If it has, the problem was probably with the circuit breaker.
  • If it hasn’t, there is probably a bigger problem, and you should call an HVAC professional to inspect your unit.

Pro Tip: Try to count how many flashes happen in one sequence — these are often codes that indicate what the problem is.

Why Is My Thermostat Blinking "Cool On?"

Is your AC not blowing any cool air but your thermostat is flashing "Cool On?" All this means is that the temperature inside your home matches what your thermostat is set at. Because your AC no longer needs to push out cool air when the temperature matches what the thermostat is set for, it creates a time delay and your compressor shuts off.


To test that this is what is causing your thermostat to flash "cool on," you can lower the temperature on your thermostat by a few degrees. If the blinking message stops and your unit kicks back on, there's nothing more to do. However, if you notice that your AC has stopped cooling or that it is cycling frequently, it could be that your AC is short cycling and needs to be repaired

Call Now for Thermostat Service in Fairfax

Many HVAC issues are the result of a bad thermostat. If you have noticed that you are constantly having to adjust your thermostat, chances are it should be serviced. At Air Treatment Company, we have the expertise needed to diagnose any and all problems you may have with your HVAC system and offer comprehensive thermostat repair and installation services. We install only quality brands so that you can enjoy reliable home comfort.

For more information or to schedule a service, give us a call at (703) 270-0881.

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