Why Is My Honeywell Thermostat Blinking Heat On?

Thermostats are essential home appliances that maintain room temperatures. But have you ever noticed that the thermostat is constantly blinking the HEAT ON? When this happens, it likely means an issue with the thermostat or the heating system.

If a Honeywell thermostat is blinking “Heat On,” it means that it is set to heat and calling for heat. However, due to some reasons, the heating system is not operating normally. Some common problems include a dirty air filter, low gas pressure, or a malfunctioning furnace.

It is essential to figure out why the thermostat is constantly blinking the heat on. This article shares all the possible reasons behind a thermostat blinking heat on and how to troubleshoot the problem. So, let’s get right into it without further delay.

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What does the HEAT ON blinking mean in the Honeywell thermostat?

All thermostats, including the Honeywell thermostat, have two indicators: COOL ON and HEAT ON.

The HEAT ON indicates there has been a delay in receiving enough heat. 

It will blink for 4 to 5 minutes, then turn on the heat to protect the HVAC from short cycling.

But, if the thermostat blinks for more than 5 minutes, there is some problem with your thermostat. 

After consulting with an expert, I learned a few common reasons behind a HEAT ON blinking for more than 5 minutes.

In the following sections, I will share those reasons and explain each in detail.

Also read: Why Is My Honeywell Thermostat Flashing Cool On?

Wrong thermostat settings 

When the temperature in the thermostat is set incorrectly, the thermostat will blink the HEAT ON. 

It happens when you don’t set the thermostat to the desired temperature. 

The blinking indicates that your room needs more heat for the desired temperature.

Ensure you set the temperature slightly above the room temperature to stay comfortable.

Another set is the HEAT and COOL settings. 

If the setting is COOL or OFF, your thermostat will constantly blink the HEAT ON for a comfortable room temperature. 

For proper warmth, you should switch the thermostat setting to HEAT. 

If that’s not the setting, the heat on blinks, demanding more heat for a comfortable room temperature.

Also read: 9 Reasons Your Honeywell Thermostat Not Turning On

Wiring issues

A loose wire is one of the common reasons behind the Honeywell thermostat blinking the HEAT ON. 

When the thermostat blinks the HEAT ON, your device is in a 5-minute delay to give you heat. But more than 5 minutes is abnormal.

The device increases the delay when the wires are loose and fail to signal your HVAC properly. 

Ultimately, the thermostat will constantly blink the HEAT ON. 

A damaged wire can also cause the heat to blink. 

So, open the thermostat cover and check the wire connections. 

If they are loose, tighten them properly. 

For damaged wires, call a professional for a replacement.

Also, check whether the wires are correctly connected or not. 

Here is a small guide to the primary wires in the device and where to connect them:

  1. Rc and Rh will be in the R terminal. The Rc is a switch for the cooling system, and the Rh is for heating.
  2. W wire will be in the W terminal. It controls the heat.
  3. Y wire controls the cooling system and the compressor. Connect it to the Y terminal.
  4. C wire is the return path of the transformer. Find the C or common terminal for this write.
  5. O wire should go to the O terminal. It is for switching the pump back and forth from cool to heat and vice versa. 
  6. G wire controls the fan and connects to the G terminal. 

Also read: What Happens If You Wire A Thermostat Wrong?

Electrical issues

Power outages and voltage fluctuations are also responsible for the Honeywell thermostat blinking the HEAT ON. 

Once, I had this problem with my Honeywell thermostat. 

I was unable to detect the problem at first. 

But after experiencing this a few times, I contacted our local electrician. 

He told us that the power outage was what caused the problem.

The thermostat starts flashing the HEAT ON after the compressor runs when the current comes back suddenly after a power outage or the voltage fluctuates. 

It creates pressure on the compressor and leads to the blinking of the HEAT ON in the thermostat. 

The problem is usual, and you cannot reverse it. 

Once the power returns, give the compressor time to work as normal as before. Soon, the blinking light will turn off.

Battery problems 

If your Honeywell thermostat is blinking the HEAT ON, the problem might be in the battery. 

The level might be low; you must replace it before it dies.

To prevent your Honeywell thermostat from blinking the HEAT ON, replace the battery regularly, every 10 months, or once a year.

To replace the battery:

  1. Turn off the device and the breaker.
  2. Open the battery compartment and replace the batteries.
  3. Remove all batteries and replace them with strong AA batteries. 
  4. Cover the battery compartment and turn back the power. 
  5. Check the thermostat to see if there is any more blinking.

Heat anticipator issues

The heat anticipator is mainly found in the old Honeywell models. 

Setting it incorrectly will make the device blink the HEAT ON. 

The heat anticipator determines how long the heating system should run after the thermostat reaches the desired temperature. 

It will either short cycle or won’t allow your HVAC to reach the desired temperature. That is why the thermostat blinks the HEAT ON. 

To fix the heat anticipator:

  1. Turn off the breaker and the thermostat, and open the device’s cover.
  2. Find the anticipator at the center of the device. 
  3. You will see LONGER or LONGER CYCLES written over it. 
  4. If the temperature is not reaching the desired temperature, adjust the level by removing the lever away from the LONGER setting by one calibration mark. 
  5. Cover the thermostat and turn back the breaker. Check the thermostat. 
  6. If the problem remains, call an expert for help.

A dirty or faulty sensor

The sensor is one of the main components of the thermostat. 

It helps the device to detect the surrounding temperature and then provides readings on the screen. 

If the sensor is dirty or faulty, it will fail to determine the correct readings of the surroundings, leading to wrong readings.

It disrupts the sensor’s ability to read the temperature. 

As a result, the device will be blinking the HEAT ON, indicating the room needs more heat.

Check the sensor to fix the problem.

If the sensor is dirty, try cleaning it by blowing air slowly or using a brush or cloth to remove the dirt and debris. 

If the sensor is faulty, you must hire an expert to replace the sensor. Make sure you are choosing a compatible one.

Thermostat malfunctioning 

When the device malfunctions, it keeps providing you with the wrong temperature readings and detection. 

For example, it will detect freezing weather at one moment and give you low-temperature readings. 

So, it will constantly indicate the need for heat by blinking the HEAT ON.  

You need to call an expert to repair the thermostat or replace it with a new Honeywell thermostat. 

Also read: 11 Reasons Why Your Honeywell Thermostat Is Blank

Wrong readings

Wrong readings are one of the main reasons behind the thermostat blinking heat on. 

For example, your thermostat is located where cold drafts are typical, like near an open or cracked window. 

So, the thermostat chills down quickly and gives you low-temperature readings. 

But your room might be as cold as the reading says. 

So, this is a wrong reading. 

Even when the room temperature is comfortable, the thermostat will demand more heat by blinking the HEAT ON. 

You need to fix the problem by placing the thermostat in the central location of your house, away from open windows, cold drafts, and sunlight. 

Switching from COOL to HEAT 

When you switch suddenly from cool to heat, the compressor is at a constant pressure. 

It flickers when the compressor is under pressure and constantly trying to give you enough heat. 

That is when the thermostat will blink the HEAT ON, indicating the need for more warmth.

The same occurs when you change from heating to cooling.

So, give it some time until you receive enough heat. 

The blinking will stop automatically when it receives the desired temperature. 

For an easy fix, try to reset the thermostat once. 

Please turn off the thermostat for 30 seconds and turn it back.

It will take 10 to 15 minutes for the system to restart.

Clogged coils

The HVAC system is the culprit here, but the thermostat gets affected.

Clogged coils of the heating system make the thermostat blink the heat on. 

With dirty coils, the HVAC system restricts the airflow. 

It remains trapped inside the unit.

As a result, your room does not receive enough heat, and the thermostat keeps blinking the HEAT ON, indicating a delay in receiving adequate heat.

Clogged filters can affect the overall performance of the Honeywell thermostat. 

So, you must clean or replace the heating system every 3 to 4 months. 

To change or clean the furnace filters:

  1. Please turn off the furnace switch and its breaker.
  2. Remove the filter and check it by seeing through it.
  3. If you cannot see through it, replace it with a new one.
  4. If the filter is reusable, wash it with water, dry it, and put it back into the heating system.
  5. While reinstalling the filter, install it in the direction of the arrows. That will allow the airflow to pass through correctly. 
  6. Close the furnace, turn it back, and check the thermostat. 

If the problem remains, call an expert for help. 

Check the HVAC system

It is common for the thermostats to blink the heat on when the HVAC breaker has tripped

When the HVAC is not in use, the thermostat will blink the HEAT ON for more than 4-5 minutes, indicating a delay in the warmth. 

So, check the breaker and flip it to turn it back. 

Also, check the furnace power switch near the unit and see if it is turned on. 

Compressor failure and shutdown 

When your Honeywell thermostat is blinking the HEAT ON despite staying in the HEAT mode, the safety timer in the compressor has tripped. 

The problem will be solved after you reset your thermostat. 

Once the safety timer problem is fixed, your thermostat should stop blinking the HEAT ON. 

The device will again be able to maintain the right temperature. 

High limit or low limit on

These two limits are safety features in the thermostat that prevents the heating system from overheating or working at a low temperature.

When the temperature is above the high limit, the thermostat turns off the heating system to avoid overheating and other damage. 

But this can affect the Honeywell thermostat in a few ways:

  • The device won’t keep the house at your desired temperature because the system will work once the temperature falls below the high limit or rises above the low limit setting.
  • The device will show error codes and messages indicating it has reached the high-temperature or low-temperature limit. 

As a result, these safety features get tripped to save the device from damage.

In such conditions, the HEAT ON of the Honeywell thermostat will blink. Resetting the device can fix the problem. 

But it is better to hire a professional to inspect the heating system to ensure it functions properly in the future without any issues.

Final thoughts

If you have reached the end of the article, you have learned all the possible causes. I hope this article helps you to identify the problems and solve them. 

When the heat blinks 4-5 times, it is normal as it indicates a time delay of the heat. But more than 5 minutes indicates a problem. The problems mentioned in the article are common reasons behind the constant HEAT ON blinking. 

If you cannot find the solutions, call an expert for help. Some issues like power outages, voltage fluctuations, shifting from COOL to HEAT, or safety features triggered are cases that cannot be reversed. Wait for some time, or reset your thermostat to fix the blinking.

Why is my Honeywell thermostat blinking?

One common reason behind a Honeywell thermostat blinking is low batteries or a loose connection in the C-wire. Change the batteries before they die and check whether the C-wire is correctly connected to the terminals.

Can a worn-out furnace make the HEAT ON blink?

Like other appliances, the furnace will also wear out over time. As a result, it won’t be able to provide enough heat. So, the thermostat’s HEAT ON keeps blinking. So, replace the furnace.

Reference: Thermostat Wikipedia

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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