Skip to Content

Furnace Overheating: All You Need To Know

Worried about the burning smell coming from your furnace but can’t figure out what’s wrong? It can be quite bothersome if the furnace stops functioning properly, especially in the freezing winter.

Why is your furnace overheating?

Furnaces can overheat due to restricted flow of air, or even due to dirty internal components. Moreover, furnace short cycling is a major reason for overheating. It could also be a broken glass regulator or a mechanical failure. Otherwise, it can be that your furnace has become old.

That’s not all. To get deeper into the overheating issue, continue reading our detailed discussion about furnace overheating solutions.

Furnace Overheating Symptoms

Furnace overheating can actually damage the entire heating system. And that’s not all, it can get worse in the blink of an eye. To understand if the furnace is actually overheating, it’s vital to be able to detect the signs of furnace overheating. Which are:

  • Constant burning aroma
  • Strange humming noise
  • Furnace turns off before finishing one complete cycle

Furnace Overheating: Causes & Solutions (6 common troubleshooters)

Fixing the overheating furnace immediately is as necessary as fixing the running toilet at your home. Because both of these issues can worsen.

To fix the furnace overheating, you’ll first need to identify the problem and then solve it. So these are the common problems that usually result in a furnace overheating.

Troubleshooter 1 of 6: Restricted Airflow

Restricted airflow is the most common reason why a furnace gets too hot. Poor air circulation can damage the components of a furnace. This is because a dirty air filter can block airflow. The trapped debris restricts the amount of air traveling through the filters, further overheating the furnace.

Moreover, blocked return vents or dirty blower wheels can also cause restriction of air.


To avoid the filters getting clogged, clean them regularly. Moreover, the furnace air filters need to be cleaned and changed frequently over a year. This keeps the furnace functioning.

1 to 2-inch filters should be changed every 3 months, 4-inch filters every 6 months and 5-inch filters once a year. That’s how often you need to replace these filters to keep your furnace in good shape.

Getting a proper venting option can be the best solution in this case.

Troubleshooter 2 of 6: Dirty Components

The clogged air filters cause the filter’s internal components to become dirty. For example, the motor could get dirty and unable to ventilate itself, further overheating the furnace. In the same way, the coil in the furnace could be filled with dirt and grime preventing the heat exchanger from moving heat. All of this results in an overheated furnace.

Clogged sensors can bring another problem. This can make your furnace go out abruptly after the blower starts. This phenomenon can be caused by the furnace overheating as well.


Again, it all comes down to cleaning and changing the air filters of the furnace. Regular maintenance of the internal components is also vital to keep the furnace working.

Troubleshooter 3 of 6: Short Cycling

Short cycling occurs when the furnace constantly turns on and off. This damages the furnace motor and prevents it from heating up the house. Short cycling can be pretty bad for a furnace as it can cause mechanical failure.

Now short cycling can occur due to a malfunctioning thermostat, a clogged flue, or a dirty flame sensor. You see how each component of the furnace affects the other. Just as one bad outlet affects others. Moreover, an oversized furnace can also cause short cycling. All of these, at the end of the day, overheats the furnace.


For a furnace that is short cycling, figure out why it is happening in the first place. If it’s a malfunctioning thermostat, it’s either placed in the wrong spot or the battery is dead. Check the thermostat and change its position to a suitable one.

For a faulty battery, get new ones for replacement.

If the furnace is short cycling due to clogged flue or a dirty flame, you’ll need to clean or repair it.

In the case of an oversized furnace, there’s nothing you can do except consulting an expert.

Troubleshooter 4 of 6: Broken Glass Valve

For a gas furnace, the overheating could be due to a broken glass valve. The glass valve, also known as the gas regulator, determines the amount of gas that enters the furnace. This keeps the furnace at the right temperature.

A broken gas regulator won’t be able to control the amount of gas entering in. Too much gas increases the flame size. This provides more heat causing the furnace to overheat.


Now for a broken gas regulator, there’s nothing you can do to fix it. So, replace the glass valve. Replacing a glass valve can be tough, thus do it carefully.

Here are our top choices of gas furnace glass valves-

Troubleshooter 5 of 6: Mechanical Failure

Your furnace can overheat due to failed mechanical parts in the system. If your furnace overheating smells of burning dust, it can be due to a short circuit or inadequate circulation.

Now, this happens because components like the electrical wirings such as a 12-2 wiring and fan blower in the furnace are often under extreme stress. The damaged components result in the failure of capturing heat.


Now it is very important to schedule regular tuning and cleaning of the furnace’s components. Moreover, look for strains and tear ups in the components. If you find damaged components, get them replaced right away.

Troubleshooter 6 of 6: Old Age

Last but not the least, if it’s not your new furnace overheating, maybe it’s become old and faulty. Furnaces are typically built to last for 15-20 years.

So a furnace that old could start overheating and stop working.


At this point, you can either repair your overheated furnace or get yourself a new one. Make sure to buy the right furnace for your home this time.


Can a furnace catch on fire?

Yes, a furnace can catch on fire. If your furnace’s gas pressure is too high, it can crack the heat exchanger.

How hot can a furnace get?

A furnace can get up to 170 degrees Fahrenheit if combustion occurs. It can be very dangerous in that case. It might even start a fire even like a gas fireplace turning on by itself.

How long does a gas furnace run?

A gas furnace can run for 10-15 minutes if there are no external factors involved.


Furnace overheating is an actual problem that can worsen real quick. So it’s important to understand its cause and fix it immediately.

We hope you can detect and solve the issue after reading our article.

Good luck!