Why Is My Honeywell Thermostat Flashing Cool On

Posted by: Mas Broto
Last Udated:

If your Honeywell thermostat is flashing “Cool ON,” you don’t need to worry or freak out. You will probably see words that blink to show that it’s in cool status. To fix a Honeywell thermostat flashing cool on, just set the temperature to the lowest setting and then reset the thermostat.

When the “cool on” light on your Honeywell thermostat starts to flash, it’s usually nothing to worry about. Most of the time, this means that the air conditioner is starting to work. But if your Honeywell thermostat keeps blinking “cool” for long periods of time and your air conditioner is not blowing cool air, you might have a problem.

There are a lot of different factors that could be wrong with your Honeywell thermostat. In this article, we’ll explain why this is happening and show you a few things you can do to fix the problem.

Reasons Why Honeywell Thermostat Flashing Cool On

When your Honeywell thermostat is flashing cool on repeatedly, it means that there is a problem. Here are the main reasons why the “Cool On” light is blinking on your Honeywell thermostat:

The battery of the thermostat is low.

When the cool light on your Honeywell thermostat keeps flashing, it may mean that the batteries are running low. The new thermostat has separate lights that show when the battery is low, but the old one still shows when the battery is low by flashing a message.

On average, thermostat batteries last for 10 months, so it’s easy to tell when the problem is dead batteries. If you have just replaced your batteries, the Cool On display may also flash on your Honeywell thermostat for a few minutes.

A power outage.

A power outage or other interruption with a power source can cause the thermostat’s compressor to start up again and the “Cool On” icon to blink. After a power outage, you may need to turn off the power to your Honeywell thermostat for up to 30 minutes to reset your HVAC system and Honeywell thermostat.

Switching of AC system from cooling to heating.

When you switch your air conditioner from cooling to heating (or vice versa), you put a lot of pressure on the compressor, which can make the thermostat blink. Simply wait 5 minutes and adjust your thermostat to see if it starts to work again.

If the 5 minutes pass up and you’re not feeling any cool air, set the thermostat to its lowest setting, wait at least 10 minutes, and then check again to see if everything is back to normal. Remember that it should be on “cool” status and that the fan should be set to “auto.”

How do I reset my Honeywell thermostat?

With time your thermostat might lose some settings or need a factory reset. If your thermostat is blinking cool on message, then you should reset your thermostat once. Resetting a Honeywell thermostat is very simple as follows:

  1. Switch off your Honeywell Thermostat.
  2. Remove the batteries
  3. Place the battery in the wrong way, place negative to the positive side and positive to the negative side for 5-10 seconds.
  4. After 10 seconds, reinsert the thermostat battery the right way. Your Honeywell thermostat reset is done, and it should be back to normal operation.


This Honeywell thermostat flashing “Cool On” message may only flash for a short time sometimes. If the light stops flashing after 5 minutes and the cool air comes back on, you don’t need to worry. This part of the unit is actually a built-in safety feature in your smart thermostat. It is meant to give your compressor about 5 minutes to start up all the parts of the system.

If you’re still having no luck solving the Honeywell thermostat flashing cool on, it’s always better to call professionals to resolve the problems.

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Mas Broto
Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.