It’s been just few months and my Honeywell thermostat flashing cool on but not cooling. It’s not working properly, how should I fix cool on error?

Is your Honeywell thermostat flashing cool on and, it is not able to regulate the temperature? Sometimes it happens that your thermostat is showing cool on message but, no air is flowing.

A thermostat is a device that is used to regulate the temperature whenever the desired temperature of a room is exceeded beyond the limit.

But, sometimes the thermostat stops working, or flashes some message, or becomes dead. The thermostat flashes “cool on” but, it’s not cooling.

If your Honeywell thermostat is also flashing “COOL ON” or “HOT ON” but it’s not working then, don’t worry! With possible solutions, it can be fixed.

You just have to follow very simple steps. Keep reading this guide for a better solution.

We will first start the discussion with WHY? Why thermostat is fleshing “cool on” or “hot on” messages, what are the possible cause, and how to resolve this issue?

also read: nest thermostat blinking red

Honeywell Home Wi-Fi Thermostat


My Honeywell thermostat is flashing “cool on” – what does it mean?

honeywell thermostat cool on flashing

If your thermostat is flashing a “cool on” message on the digital display, then the thermostat is in delay mode which might take up to 5-10 minutes to get recovered.

This delay is an in-built feature of every thermostat. It is used to protect your equipment from short cycling. Otherwise, it will affect your HVAC system.

So, it’s not a time to get panicked or worried! It will be recovered within the next 5-10 minutes. And, again it will start working normally.

In case, the flashing doesn’t stop automatically, then you have to check the source of the problem to get it recovered.

So, in the next heading, we are going to see the most common source of problem due to which your thermostat is flashing “cool on”.

Why honeywell thermostat flashing cool on?

The cool on flashing on Honeywell thermostat is usually stable and does not flash. In case, it is flashing for more than 5-10 minutes and doesn’t stop after that, then Air Conditioner is interrupted or have some technical fault.

The battery of thermostat is low

Sometimes, the Honeywell thermostat cool on flashing indicates the low battery power of your thermostat.

The modern thermostat has separate indicators that indicate the low battery but, the old thermostat still indicates the low battery by flashing some message.

Compressor has been restart within short period of time

If you have changed the temperature manually, then it will force the compressor to restart due to which your thermostat will start flashing some message.

Switching AC mode from hot to cool or cool to hot

Sometimes, it has been observed that the thermostat flashes “cool on” when there is a sudden change from cool to hot or from hot to cool.

This sudden change force compressor to restart and affect the HVAC system.

Power cut

Your thermostat might be blinking due to a power cut. Power cut forces the compressor to restart due to which the thermostat starts flashing.

Issue with the C wire

Also, check the C wire if it is broken from any point. A broken wire will surely cause your thermostat to blink.

Let’s fix the COOL ON blinking of Honeywell thermostat

Now, let’s fix the flashing problem of the thermostat. Kindly note, it’s always better to call professionals to resolve technical problems.

But yes, there are some of the things that you can check on your own before calling a technician.

Don’t worry – wait

Yes! Believe it or not, but some problems get automatically get recovered when you wait.

If you had restarted the compressor, switches the AC mode, or there is a power outage, then wait for at least 10 minutes.

In these 10 minutes, the system will automatically get recovered. If it’s already more than 10 minutes, it’s time to take action.

Set the thermostat to the lowest temperature

If you have already waited for more than 10 minutes and your thermostat is still flashing “cool on”, it’s time to take action.

The very first thing that you can do is to set the thermostat to the lowest temperature, then again wait for at least 10 minutes, and finally, check if it’s normal now.

Keep in mind that, it should be in “cool” mode and the fan setting is set to “auto mode”.

Check if your thermostat is in “Setup mode” or if the clock is on

If the power outage occurs very recently, then check your thermostat mode. Is it in Setup mode or clock is set? Now, you can use the Honeywell manual to set up your thermostat accordingly.

Check if the batteries are too low

Check if the battery of your thermostat is charged enough. If the battery is low charged, then it will blink some messages on the thermostat display.

If the batteries are too low, then it’s better to change the batteries of your Honeywell thermostat.

Check if your appliances are getting enough power

If your AC is not getting the required amount of power, how would it start? It will definitely force your Honeywell thermostat to blink “cool on”. Check all the plugs, appliances, c-wire. If any of them seems disturbed, kindly fix it.

last but not least, Reset your Honeywell thermostat

If Honeywell thermostat flashing cool on even after changing batteries so, you can simply reset the Honeywell thermostat.

How do I reset my 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 thermostat is very simple. Now, there are various types of thermostats in the market. And, all of them have different ways of resetting.

The best way to reset your thermostat is to read the manual of your thermostat. In that manual, you’ll surely get something that will help you to reset otherwise you can read the article on “How to reset the Honeywell thermostat”.

Honeywell thermostat won’t change temperature – what should I do?

This is another problem that most people face. “I changed the temperature but, it is not changing”. Are you also facing the same kind of problem? So, don’t worry! We will resolve this issue also.

I have written a complete blog that discusses why your Honeywell thermostat is not changing temperature. If you want to read it, feel free to read it!


I hope it was a helpful guide for the Honeywell thermostat “cool on” flashing issue. We did all the possible research from entire the internet to give you the best resolution of your problem.

It’s not last, the discussions are always open in the comment section below. Let us know which action helps you to stop the blinking of the “cool on” message from Honeywell thermostat.


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