Why Does Home Thermostat Say HEAT ON But There Is No Heat?

Seeing that your home thermostat says ‘heat on’ while in reality there is no heat is one of the most annoying things ever. What could possibly be wrong?

The most common reasons for such a problem are a dirty filter, thermostat malfunction, pilot ignitor, wrong settings, or low battery issue. In such a case, all you would have to do is clean the device, double-check the thermostat settings, or replace the batteries.

How to find out what exactly is wrong with your thermostat and how to avoid such issues in the future? Here is everything that you need to know. 

Common Reasons Why There Is No Heat

If the thermostat says heat on but no heat, there might be quite a few reasons for that.

The filter is dirty

Perhaps, the most common reason for such a situation is a clogged filter. All you would have to do is have a look at your filter. If the thing looks dirty, then it means that the airflow is restricted and your furnace simply can’t operate.

Dirty hvac filters

Replace the filter and see if that helps.

Ideally, you would want to get a new filter every two months or so. By the way, you won’t end up overspending – in case the filter is dirty, it wouldn’t be able to effectively heat your place up, which will result in higher bills.

The gas supply is off

Do you have a gas furnace? Then don’t forget to open the gas supply valve.

Warning! If this easy manipulation didn’t fix the problem and you started smelling gas, then turn off the gas supply and call a professional (gas leaks are a serious issue).

gas valve is off

The heater is cut off from the power source

Check your electrical panel to make sure that the power was not cut off. The next step might seem like an obvious one, but do check the power switch. Is it in the ON position?

The pilot ignitor is dirty

Another common problem that might occur, in case you have a gas furnace. If you feel comfortable working with different devices, turn off the power and take the front panel off of your furnace. Does the ignitor look dirty and clogged? Then it looks like you would have to call a professional team to fix that.

The thermostat is on the wrong setting

The problem might be with the actual thermostat. Thankfully, it’s extremely easy to check that.

Remember that, in order to activate the furnace, the thermostat has to be set to a temperature above the current room temperature. Some prefer to set the thermostat to the highest heat setting to get it going. In such a case, don’t forget to turn the thing back down before it becomes too hot.

After that, make sure that the system switch is in the AUTO or HEAT position. Also, do check whether or not the fan is set to AUTO or ON.

There is an issue with the battery

If you have a battery-powered thermostat, then that might be the problem. A weak or dying battery has to be replaced. Once you have changed the batteries, make sure to wait for a bit, so that the thermostat has some time to adjust.

As you can see, a lot of reasons mentioned above can be easily fixed even by someone who is not very good with technology. However, if you do not feel comfortable dealing with such issues and if you are not sure what exactly you would have to do, do contact a specialist that is going to take care of the problem.

How to Avoid Such Issues in the Future?

In a lot of cases, you will be able to avoid various issues with your thermostat, if the device undergoes regular maintenance.

Come up with a maintenance schedule and, as a result, your heating system is going to work more effectively and the central air system is going to last much longer.

Know when to change the batteries

When should you change the batteries?

  • Your thermostat might come equipped with a ‘low battery’ warning light, so keep an eye on that one. Or the device may start emitting a light beeping sound when the time comes to replace the battery.
  • As a rule of thumb, replace the batteries at the beginning of each new season, in order to avoid any malfunctions, when you desperately need heat or cold.
  • Make sure to change the batteries before going on vacation or a business trip to prevent any thermostat-related problems while you’re gone.

Learn how to clean the thermostat

The number one reason why your thermostat might be malfunctioning is that it is dirty. That’s why it is essential to learn how to clean the device

By the way, the thermostat might become one of the most-touched surfaces during a heatwave or cold winters. So, cleaning the thing is also essential to keep the surface free of germs.

Repair thermostat
  • Remove the cover. Some models will have screws, while others have covers that simply snap off.
  • Use a dry, soft paintbrush to gently dust the inside of the thermostat. There might be some debris in places where different electric components touch. A brush won’t really help you here. What you can do is take a dollar bill and slide it between the components like dental floss. This will help you loosen and, later on, remove any dirt.
  • Now, you are ready to inspect the wires. If you find any corroded or loose wires, make sure to call an electrician (it is dangerous to try and replace the wires on your own).
  • Replace the batteries, if you need to.
  • Dust the cover and put it back on the thermostat. Bear in mind that smart thermostats do not require interior cleaning.

Learn how to check the thermostat’s accuracy

Another thing that you would want to do is check the thermostat’s calibration. If the numbers are inaccurate, the chances are high that there is something wrong with the actual device and that might be one of the reasons why it is saying that the heat is on, when it’s freezing cold in your house.

What are you going to need to calibrate the thermostat?

A glass tube thermometer, tape, a paper towel. You might need a level and a paintbrush.

  • Tape your glass tube thermometer right to the wall an inch or two away from the thermostat. Make sure to pad the thermometer with a paper towel or a napkin to ensure that it shows the right temperature.

The devices should not be affected by outside temperatures influences. For example, sometimes the hole in the wall behind the thermostat through which the wires enter the device can be too big. In such a case, cold air is going to reach the thermostat and affect the accuracy of its readings.

  • Wait for 10-15 minutes. The mercury in the glass tube thermometer needs to stabilize.
  • Compare the readings.
  • If the variation is more than one degree, then something is wrong with the thermostat. The first most obvious thing that you can do is clean the device (see the instructions above). 

In case your thermostat has a mercury vial inside, you would have to use a level to make sure that the thing is straight. If it’s not – loosen the mounting screws and adjust the device until it is straight. 

  • Check the thermostat’s accuracy once again. If the problem persists, it looks like you would have to replace the device.

As part of your maintenance routine, you should also make sure that the air is flowing. Clean all air filters and ducts on a regular basis.

When Should You Call a Professional?

There are quite a few things that you can do on your own to fix a thermostat that displays ‘heat on’. In the majority of cases, this malfunction indicates a small issue that you can deal with in a matter of minutes.

However, such a minor problem might be an indication of a more serious issue. That’s why you should know exactly when you should call a professional as various ‘DIY’ solutions can lead to terrible consequences.

What you can doWhat you should leave to the professionals
Replace the batteries
Clean the thermostat
Clean the ducts and air filters
Calibrate the device
Check the settings
Change the filter
Gas issues
Dead blower capacitor
Low refrigerant levels
Cracked heat exchanger
Issues with the sensor
Improper ductwork

To Sum Up

Now you know why your thermostat’s display might be showing ‘heat on’ when in reality there is no heat.

Make sure to:

  • Check the settings
  • Clean the device
  • Change the filter and batteries
  • Make sure that the thermostat undergoes regular maintenance

If you follow the guidelines mentioned in this article, you will be able to fix all the minor thermostat-related problems.

Don’t underestimate the importance of regular maintenance and know exactly when to call a specialist as sometimes such small thermostat malfunctions might be indicators of bigger problems that need to be solved by the professionals.