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Why Is My Furnace Overheating? A Kansas City Tech Answers

January 31, 2019

If you hear your furnace turning off and on frequently, it’s most likely overheating. But why? There are three possible possible explanations:

  1. Your air filter is dirty

  2. The majority of your vents are closed or blocked

  3. Your blower wheel needs to be cleaned

Let’s take a look at each explanation in more detail below.


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Explanation #1: Your air filter is dirty

The most likely reason your furnace is overheating is a dirty air filter. A clogged air filter prevents your furnace from “breathing in” enough cold air. When your furnace heat exchanger (the part that heats the air) doesn’t get enough cold air passing over it, it will quickly overheat. And when your heat exchanger overheats, certain safety features will automatically shut the furnace off.

To prevent a dirty filter, get in the habit of checking the condition of your air filter monthly, and change it every three months to prevent overheating.

An example of a severely clogged air filter

This is by far the cheapest and easiest solution, but left unchecked, it may cost you future a service call.

Explanation #2: The majority of your vents are closed or blocked

Think twice before closing an air vent and putting furniture in front of or on a vent because it could be the reason your furnace is overheating.

Closing or blocking too many of your vents increases the air pressure in your ducts. This can cause some furnace blowers to slow down, which decreases airflow over the heat exchanger and can lead to an overheated furnace.

Keep all vents (supply and return) open and unobstructed.

Explanation #3: Your blower wheel needs to be cleaned

Note: Only older furnaces have blower wheels, so if you have a furnace that was installed recently, this most likely isn’t your issue.

If your air filter is clean and all your air vents are open, the next likely explanation for your furnace overheating is a dirty blower wheel. When too much residue builds up on your blower wheel, it has to work harder to circulate the air through your furnace.

A good way to tell if this is the reason for your furnace overheating is to take a look at the wheel to see if it’s dirty and/or to put your hand over the motor and feel if it’s giving off heat.

In either situation, it’s best to call an HVAC specialist to clean the wheel an/or repair it.

Need help determining why your furnace is overheating? We can help.

If you need help diagnosing a furnace that is continually overheating, we can help.

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