Heating & Cooling

Honeywell Thermostat Blinking Cool On: Causes & Fixes

Honeywell Thermostat Lg 1

Honeywell thermostats are some of the best HVAC systems on the market. These systems have a “Cool On” indicator message to inform the user that the system works to cool the environment. What if this message begins to blink on and off? You got to be asking, “why is my Honeywell thermostat blinking Cool On”?

The blinking “Cool On” message on a Honeywell thermostat display indicates that the system is restarting, batteries need replacing in the control panel, or a fault with the system. If the blinking persists for more than five minutes, contact a technician to perform diagnostics.

The “Cool On” indicator message on a Honeywell thermostat is usually constant when it is displayed. Still, when it blinks on and off, it can be disconcerting. Let’s find out why a Honeywell thermostat may have a blinking “Cool On” message and what to do about it.

Why Is My Honeywell Thermostat Blinking “Cool On”?

If the Cool On message or snowflake light is flashing, it indicates that the system is experiencing a problem, a delay, or something wrong with the system.

The message could mean something as simple as a required battery change or that the system is in a time-out session, or it could mean something more serious such as a fan malfunction.

Honeywell thermostat control panels have a Cool On or Heat On. The message is usually constantly displayed when the system is actively cooling or heating your home. Occasionally this message may change from constant to blinking. What does it mean if this message is blinking rather than constant?

There are several causes why a Honeywell thermostat may have a blinking Cool On or Heat On message. Still, it is usually not a severe issue.

However, it is still essential to understand and identify the blinking message’s cause. It indicates a potential issue that will need to be resolved.

Honeywell thermostat systems have a Cool On message or a snowflake light that both indicate the same potential issues.

Is A Thermostat Blinking “Cool On” A Serious Problem?

If the Cool On message blinks on the thermostat control panel, it is usually nothing to worry about. This message usually indicates a normal function of the thermostat system. If the blinking message persists after a long while, it could mean a more severe issue.

If the Cool On message is blinking, it usually means that the thermostat system performs a routine function that helps to protect the system from harm when various settings are changed or selected or if the system is in a particular stage of its cooling cycle.

The same is true if the system has a flashing “Heat On” message, as the indication is indicative of the same functions within the HVAC system.

This blinking message should resolve itself in a few minutes. Still, it may indicate that the system is experiencing a problem rather than performing a standard function if it persists for a while.

Let’s go over the common reasons why this message may be flashing on the thermostat display screen when concerned about it and potential resolutions to the problems that it may indicate.

What Causes The Flashing “Cool On” Message?

One of the reasons why the “Cool on” message is flashing is because your Honeywell Thermostat needs a battery change. There are several causes for the flashing Cool On message on a Honeywell thermostat, some are more serious than others, but they are all relatively simple to resolve.

Here are some of the most common reasons for the flashing indication, both serious and straightforward:

Required or Completed Battery Change 

The Cool On message on the thermostat display screen may be flashing to indicate that the control panel requires a new set of batteries, or it may flash when the batteries have just been changed.

A flashing message like this indicates the need for fresh batteries, as most thermostat systems do not have battery indicator lights or messages. The batteries in the control panel are essential to keep the panel running and effectively controlling the thermostat.

Suppose the batteries in the panel have just been changed. In that case, the message may flash on and off, indicating that the system checks the pressure within the HVAC compressor before it allows any temperature or control settings to be altered by the revived control panel.

Both of these instances are nothing to be concerned about, and the flashing will cease within a few minutes of fresh batteries being installed into the control panel.

Restarting The Compressor

All thermostat systems have a compressor unit built into them that pressurizes the system to function correctly.

This compressor is how the cooling and heating systems function, and it is required to both heating and cooling the environment.

The compressor only runs when necessary, and it is not running all the time to prolong the lifespan and effectiveness of the unit.

When the thermostat system is used to bring the internal temperature or building up or down to a specific temperature when this temperature is achieved, the compressor shuts off until the temperature must be altered again.

If you have set the thermostat to reach a specific temperature, the temperature is achieved, turning off the compressor. You happen to restart the thermostat to further cool or heat the environment, the Cool On or Heat On message will flash, respectively.

This indicates that the compressor is not yet active, and it will take a few minutes for it to turn on and perform its function.

This delay is what is known as the “time-out” feature. All Honeywell thermostat systems have this time-out feature. The feature affords the compressor enough time to equalize the pressure in the system before reactivating, which helps to protect this vital component from harm.

This is important because the intake and outlet sides of the system will be at different pressures after the compressor has been running for a time. These high and low-pressure areas must equalize before the compressor runs again to avoid damaging the system.

In this instance, the blinking message will return to a solid message after about five minutes when the system is ready to run efficiently again.

Do not be concerned if you see the blinking Cool On message in this circumstance, as it is a function that is protecting your thermostat system from damage.

Switching From Cooling To Heating, or Vise Versa

Another harmless reason for the Cool On or Heat On message to blinking on a Honeywell thermostat is if you change the system from its cooling function to its heating function or the other way around.

This flashing message is to indicate that the system is changing its configuration to switch to another function. 

The system must make various changes to its operation and switch from either cooling to heating or vice versa.

When the blinking message appears in this instance, it is nothing to worry about. This is a normal function that informs you that the system is making the change you have asked it to, and the message will stop blinking in a few minutes when the thermostat system switches to its new function.

Cooling Function Not Working

One of the more severe causes of the blinking “Cool On” message could be that the cooling function of the thermostat system is not working as it should.

This will be evident if the system does not effectively cool down the environment, there is no cool air coming from the system vents, and the blinking message does not change to solid within a few minutes.

A loss of power may cause this to the HVAC system due to a tripped circuit breaker, a problem with the furnace or compressor, or it could indicate a wiring problem or malfunction within the thermostat system or the control panel.

This is the worst-case scenario when the “Cool On” message is flashing on the display screen, and this will only be the case if the blinking lasts for longer than five minutes.

In this instance, more investigation needs to be done to identify the source of the issue. It must be resolved for the system to resume its proper function.

Resolving Non-Critical Issues

A “Cool On” indicator message may well indicate a harmless issue such as the need for a battery change, a time-out period for the compressor to restart, or a time-out period for the thermostat system to switch from heating to cooling or vice versa.

Suppose the blinking message is active while the thermostat is effectively and actively cooling the environment. In that case, the blinking usually indicates that the thermostat control panel requires fresh batteries.

If this is the case, remove the face of the control panel and replace the batteries. Replace the face panel, and the message should stop blinking within a few minutes.

If the blinking message appears after you switch the system from heating to cooling or vise versa, or if you restart the system after it has reached the predetermined temperature, then the system is most likely in a time-out period to protect the system and HVAC compressor from damage. At the same time, it makes the appropriate changes to execute the new command.

In this instance, the system will resume function in a few minutes when it has made the appropriate adjustments, and the blinking message will switch to a solid message within five minutes or so.

These possible instances are nothing to be concerned about and are normal functions for a Honeywell thermostat system.

Resolving Critical Issues

If the blinking does not cease within five minutes and persists for a long while, it may indicate a lack of power to the system, a fault or problem with the furnace or compressor, or faulty wiring.

The persistent blinking message indicates that the system is not able to function because of a specific issue. If that issue is that the system has no power, it will be evident that the system is not functioning at all, even if the setting is changed on the control panel.

This is most likely due to a tripped circuit breaker. Locate the breaker board, reset the tripped thermostat circuit breaker switch, and the system should begin functioning as usual again.

If resetting the circuit breaker is not the solution, and the message is still blinking without stopping, contact a certified Honeywell HVAC technician. This message may be indicating a serious issue with the wiring or mechanical function of the system, and it should be addressed by a professional.

That being said, this is an infrequent circumstance, and the blinking message usually indicates a normal thermostat function that is nothing to be concerned about.


The “Cool On” message on a Honeywell thermostat indicates that the system is functioning to cool the environment. The “Heat On” message means the same for the heating function.

Suppose either of the messages is flashing on the thermostat display screen. In that case, it usually means that the system is in a time-out period while it equalizes the pressure within the system to continue functioning well without causing any damage to the compressor or any other parts of the system.

The flashing may indicate the need for a battery change in the control panel if the system is functioning well. After changing the batteries, the blinking will cease.

If the message continues to flash for more than five minutes, check that the system has power. If so, there may be a problem with the system that must be assessed by a professional.

Overall, the blinking message is nothing to be concerned about unless it continues for more than five minutes at a time without stopping.

If the message returns to a solid state, the system is functioning normally as it should!


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.