Why Gas Furnace Is Overheating?

A gas furnace has a few important components that ensure that it runs well. Should these components fail or be faulty it could lead to problems like overheating.

Roughly 57% of homes in the US use natural gas for heating and more than half of the homes in Canada likewise.

Your overheating gas furnace could be a sign that one of the critical components that are responsible for the proper functioning of the furnace is failing or faulty or that you have restrictions in airflow.

To understand what you are dealing with you need to first know what a gas furnace is.

A gas furnace is a furnace that runs on natural gas and serves the purpose of heating the air in your home and its various rooms and living areas.

The gas furnace has the following critical components.

  • The thermostat  When the air in your home gets too cold, the thermostat commands the heater to turn on.
  • Draft Hood/Fan directs the air towards the burners where it combusts, warming the air for redistribution around the house.
  • Burners are metal tubes through which the natural gas travels and burners heat the incoming air.
  • Heat Exchanger is made up of metal tubes that are heated by the burners to warm the air inside of the furnace
  • The blower directs air coming in through the ducts towards the heat exchanger and then redirects it back through the ducts throughout your home
  • A flue is a vent that collects the combustion gas waste and directs it away from the home.

Symptoms of a Gas Furnace overheating

There are a few tell-tale signs that your gas furnace is overheating.

When you first turn on the furnace as the cold weather sets in, a burning smell is not unusual, this should last no longer than + – 30 min. This is just the build-up of dust and debris that have collected in the unit during the dormant periods burning away. Servicing the furnace before the winter is a good idea to eliminate these smells.

If the burning smell does not disappear, there might be something bigger brewing. The smell is usually accompanied by the furnace turning itself on and off irregularly. It is advised to immediately shut the furnace down and investigate or call a professional.

Another symptom could be the furnace emitting strange noise, strange noises in any HVAC system is never a good sign, The particular noise to listen for would be a humming noise, this is a sign that the motor is trying to do its work but is failing and will shut down completely within a short period of time.

An additional symptom that would be noticeable is when your furnace switches on and off and then does not switch on again. Furnaces have various safety devices that shut down the furnace if it gets too hot. If you must reset the furnace every time before you start it again, there are likely overheating issues, and the furnace should be serviced or repaired.

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Reasons a gas furnace is overheating

Now that we know the symptoms, the following are the most common reasons that lead to a furnace overheating and possible solutions to resolve the issues. 

Restricted Air Flow

The most frequent reason for furnace overheating is restricted air movement. Furnace components may be damaged by poor air circulation. This is because a clogged air filter may be obstructing the air passage. The quantity of air that passes through the filters is restricted by trapped debris, which raises the furnace’s temperature.

Furthermore, air flow may be limited due to blocked air vents or dirty blower fan.


Clean the filters on a regular basis to prevent blockage. Furthermore, throughout the course of a year, furnace air filters must be cleaned and replaced regularly. The furnace will continue to operate properly due to having done this.

Filters should be replaced every three months for 1-to-2-inch filters, every six months for 4-inch filters, and once a year for 5-inch filters. This is how often you should change these filters to maintain your furnace in excellent working order.

Short cycling 

When the furnace switches on and off often, it is known as short cycling. The furnace motor is damaged as a result, and the home is unable to be heated. Short cycling is harmful for a furnace since it may result in mechanical failure.

A faulty thermostat, a blocked flue, or a dirty flame sensor may cause short cycling. You can observe how each furnace component influences the others. Just as one poor outlet influences others, so does one bad component influence others. All of this, in the end, causes the furnace to overheat.


To fix a short-cycling furnace, find out why it’s occurring in the first place. If the thermostat isn’t working, it’s either in the incorrect location or the battery is dead. Check the thermostat and set it to a comfortable temperature.

Purchase fresh batteries to replace a defective one.

You’ll need to clean or repair the furnace if it’s short cycling owing to a blocked flue or a dirty flame.

There’s nothing you can do about an enormous furnace except seek advice from a professional.

Glass Valve with shattered glass

Overheating in a gas furnace may be caused by a broken glass valve. The quantity of gas that enters the furnace is controlled by the glass valve, also known as the gas regulator. This maintains the proper temperature in the furnace.

A faulty glass valve/gas regulator will be unable to regulate the quantity of gas entering the system. When there’s too much gas in the tank, the flame becomes bigger. This adds additional heat to the furnace, causing it to overheat.


There’s nothing you can do about a faulty gas regulator. As a result, the glass valve/gas regulator must be replaced. Replacing a glass valve/gas regulator may be difficult, so proceed with caution.

Mechanical Failure 

Due to faulty mechanical components in the system, your furnace may overheat. It may be due to a short circuit or insufficient circulation if your furnace is overheating and emitting a burning dust odor.

This occurs because components such as electrical wire, such as a 12-2 wiring, and the furnace blower fan are often subjected to severe stress. 


It is essential to arrange frequent servicing and cleaning of the furnace’s components. In addition, check for damages to the components. If you discover any damaged components, replace them immediately.

Age Of The Furnace

Finally, it might be that your furnace is old and defective. 

Furnaces have a life expectancy of between 15 and 20 years.

As a result, an outdated furnace may overheat and cease functioning properly.


You have the option of repairing or replacing your furnace and selecting the right furnace for your house is important.


1.Is it possible for a furnace to catch fire?

Yes, it is possible for a furnace to catch fire. If the gas pressure in your furnace is too high, the heat exchanger may crack and cause a fire

2.What is the maximum temperature that a furnace can reach?

If combustion happens, a furnace may reach 170 degrees Fahrenheit. In such scenario, it may be very hazardous. It might even start a fire, like a gas fireplace that turns on by itself.

Overheating in the furnace is a serious issue that may quickly escalate. As a result, it’s critical to figure out what’s causing it and repair it as soon as possible, having a good Checklist for Gas Furnace Inspection will go a long way in assisting in the process.