Honeywell Thermostat Says Heat On But No Heat?

Benjamin Wright
by Benjamin Wright

Honeywell thermostats are beloved for their fair price, useful settings, and effective interface. They especially come in handy during winter when you need to adjust the heat and enjoy your furnace. So, what does it mean when your Honeywell thermostat says “Heat On” but there is no heat?

A Honeywell thermostat can say “Heat On” when there is no heat if the furnace filter or fan blades are clogged. The thermostat will say that it’s heating without the furnace kicking on if your temperature sensor is damaged or broken. Low batteries can also cause inaccurate readings and prevent your Honeywell thermostat from sending signals to your furnace.

In other cases, it is as simple as waiting 5 minutes while the compressor resets before the heat kicks on. Luckily, the solutions for most of these problems are simple fixes and many don’t require professional help. Follow along as we explore what it means when your Honeywell thermostat says “Heat On” but the heat won’t work.

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Possible Reasons Why Your Heat Won’t Come on

You can’t fix your Honeywell thermostat until you diagnose why it says “Heat On” but there is no heat. Solutions range from waiting it out to spending hundreds on repairs depending on the problem. There are many reasons why a Honeywell thermostat can say the heat is on without heating the house, such as:

  • Dirty fan blades
  • Temperature settings
  • Faulty sensor
  • Low battery
  • Clogged furnace filter
  • Compressor protection

Luckily, most of the reasons that your Honeywell thermostat will malfunction in this way have simple fixes. Let’s take a look a the main causes for an inaccurate “Heat On” reading on your Honeywell thermostat.

Dirty Fan Blades

An AC fan is an important part of an HVAC system, and problems with the blades or motor can affect your thermostat. Debris and dust accumulate on fan blades, and they eventually work less efficiently. The heat won’t turn on even if you program your Honeywell thermostat to heat if there is a clog in the fan blades.

Dirty HVAC fan blades can also increase your energy bills. It is a waste of money and energy to turn the heat on when your HVAC fan blades are dirty, and your Honeywell thermostat won’t work well until you clean them. The dust and debris that builds up on HVAC fan blades can worsen the air quality in your home and trigger allergies.


It is ideal to hire an HVAC professional to clean your fan blades, but a DIYer can do it with a few household tools. You can clean HVAC fan blades with a screwdriver, rags, and a vacuum. You need to turn off your air conditioner and furnace before you clean the fan blades.

Remove the top of the fan assembly with a screwdriver so that you can easily access the blades. Mix mild dish soap with hot water and rinse the fan blades to remove thick dust, dirt, and debris from the fan blades. You can also use a hose, but you may not be able to access hot water in that case, and cold water is less effective.

Clean your AC fan blades every other year so that work properly they don’t get clogged. However, many professionals recommend that you clean the blower assembly once per year.

Temperature Setting

You can throw your Honeywell thermostat off if you set it to a temperature that it can’t reach. Each HVAC system has a threshold, and it cannot keep up if you set the thermostat too high. That doesn’t indicate a problem with your thermostat, but it does show that you need to adjust your temperature settings.

This is most common during extremely cold temperatures when an HVAC system has to work harder. You won’t be able to make the heat work if you simply keep increasing the temperature in this case. Doing so will simply waste energy and increase your bills without heating the housing up.


You can improve your HVAC’s performance if you adjust your Honeywell thermostat’s temperature. Experiment with the temperature settings on your thermostat on a cold day. Increase the temperature until you notice that your HVAC system can’t keep up with it or get warmer.

For example, if your system won’t increase the heat past 75 degrees, simply don’t program the temperature higher than that. Never exceed the temperature threshold on your Honeywell thermostat once you discover it or else you will just waste money. Remember, just because your thermostat lets you program a high temperature doesn’t mean that your HVAC system will respond to it.

Faulty Sensor

Honeywell thermostats contain a sensor that reads the temperature in the room and delivers a signal to the furnace to heat the home. Problems with a thermostat signal can delay or prevent communication with the furnace. A faulty thermostat sensor can also send incorrect signals to the furnace and it may say that the heat is on when it isn’t running.


Generally, the only solution to a faulty thermostat sensor is to replace it. You can replace your thermostat sensor for an average of $77 if you buy the part. Professional thermostat sensor replacement costs $171 on average, but it can cost as little as $140.

Low Battery

Batteries last for an average of 10 months, and they can cause your Honeywell thermostat to perform poorly as they’re dying. The batteries in your thermostat can cause glitches such as inaccurate readings and hinder your HVAC system’s functions. A Honeywell thermostat may read “Cool On” or “Heat On” if the batteries are low.

Honeywell thermostats will cease to work when the batteries die unless it is also hardwired. Even still, a thermostat will work better if it is hardwired and you use batteries. Your Honeywell thermostat can also malfunction if you put incompatible batteries in the compartment.


Replace your batteries when you notice they are low so that it doesn’t affect your temperature settings. Try not to wait to change batteries until it’s too late because your Honeywell thermostat will temporarily quit working. That way you won’t have to worry about going without heat or cooling if your batteries die altogether.

Make sure that you replace the batteries with the same kind so that your thermostat will work properly. The average Honeywell thermostat requires AA batteries, and they can last up to 12 months. However, pay attention to your thermostat after 10 months because your batteries may show signs that they are weak.

Clogged Filter

Furnace filters are just as likely to clog with dust and debris as HVAC fan blades. Winter is especially harsh on furnace filters, and your furnace will struggle to heat the home if the filter is clogged. Small furnace filters can clog within 3 months, but the average 6” filter may take 12 months to become clogged.

A clogged filter will make your furnace work harder with less effective results. Homeowners often try to compensate by increasing the temperature, but that does not work. High energy bills with ineffective heating can indicate that you have a dirty furnace filter before you even inspect it.


You can remove dust from a furnace filter with a cloth or brush, but it is ideal to replace it. Furnace filters wear out over time as they get dirty or clogged, and professionals recommend you replace your filter every 3 months. However, the average homeowner replaces their furnace filter once per year, and that is generally fine.

Compressor Protection

Honeywell thermostats can read “Cool On” or “Heat On” without working to protect the compressor. This built-in function can trigger when you turn the heat back on too soon after the system turns off. Otherwise, your compressor can overload, and it may break from too much pressure and overuse.


All that you need to do is wait 5 minutes for your compressor to be ready to run again. The heat should start working again and your Honeywell thermostat will work as usual. However, you can tell that there is something else wrong if the heat doesn’t work after the 5 minute waiting period.

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Related Questions

Why is my Honeywell thermostat showing auxiliary heat?

The “auxiliary heat” message on a Honeywell thermostat indicates that your heat pump struggled to heat up. This generally occurs in extreme cold temperatures when the heat pump works to reach the temperature that you program. Your thermostat will read “auxiliary heat” when the temperature drops to 2 degrees below the temperature that you programmed.

Why is my Honeywell thermostat blinking cool on?

A Honeywell thermostat blinks “cool on” if the batteries are dying, the blower motor is bad, or the air filter is dirty. The message can also appear if the thermostat was improperly installed or if the wires are damaged. Honeywell thermostats also display a “cool on” message if the compressor needs 5 minutes to reset.

Summing It Up

A Honeywell thermostat can read “Heat On” when there is no heat if the batteries are low are dead. Dirty or clogged furnace filters and HVAC fan blades can prevent the temperature from reaching your preferences. Sometimes, you only need to wait 5 minutes for the compressor to cool down before your furnace will turn on and heat the house.

Otherwise, you may need to replace your Honeywell thermostat’s temperature sensor. Your thermostat can also read “Heat On” if your HVAC system cannot keep up with the demand in extremely cold weather.

Benjamin Wright
Benjamin Wright

Benjamin is a proud homeowner who loves to write about DIY projects and home improvement projects. Traveling, perfecting his home, and spending time with his family are just a few of the many things that keep him inspired.

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