Furnace Overheating: Why It Could Be Happening

San Rafael

(415) 942-6565

Santa Rosa

(707) 452-3464

Any kind of furnace problem is always troublesome, but an overheating furnace can be especially worrying. Not only will an overheated furnace lessen the efficiency of your heating system, but it could also lead to dangerous problems within your home, like fire hazards. Also, if left untreated, you could find yourself having to deal with costly repairs.

Read on to find out what the warning signs of an overheating furnace are, as well as the different reasons it could be happening, and what your options are to prevent it from continuing or happening again in the future.

Signs Of An Overheating Furnace

  • Burning smell: While the initial burning odor after a period of no use is normal for any furnace, the aroma continuing on for an extended period of time is not a good sign. This means the wires and components could be damaged by the furnace overheating.
  • Strange noises: Odd noises in furnaces are never a good sign. Apart from the usual light humming noise a furnace will make while running, hearing loud noises, such as banging or clanking, could mean that the internal components, like the motors, are being overworked and possibly malfunctioning.
  • System shuts down suddenly/Furnace short cycling:If your furnace is overheating, it could cause the system to shut down unexpectedly or only go through very brief cycles. The furnace turns off randomly like this because of mechanisms in place that will shut the system down once overheating is detected.

Reasons Your Furnace is Overheating

1) Restricted hot air flow

The warm air produced by your furnace must pass through the air filter before traveling through a series of ducts. If there is a blockage within the ductwork or the air filter, this blocks airflow and can cause heat to build up with no area to escape due to the obstruction. This can lead to the internal temperature increasing rapidly within the furnace unit and the system overheating.

2) Too many closed vents

If you have a number of closed vents throughout your house, this causes a similar problem, with the trapped hot air having nowhere to go and causing the HVAC system to strain itself in an attempt to push heat through the blocked vents. Just having a handful of vents closed or blocked can cause overheating.

3) Poor maintenance

Every HVAC system will deteriorate over time without regular maintenance to ensure parts are in proper order and debris is not building up. If maintenance is not done, parts can become worn and faulty, which could lead to things like a stressed fan blower causing a short circuit in the system. This will significantly lower circulation, and the furnace will overheat.

4) Failed protection mechanism/fault wiring

Furnaces typically have some type of protection mechanism that shuts it off when it is about to overheat past the maximum operating temperature (hence the possible problem of your furnace shutting off unexpectedly) and gives the furnace time to cool off. But if this mechanism is faulty, it could cause the heater to overheat and seriously harm your furnace. Another of the most common causes of a furnace overheating is any kind of faulty wiring or inner mechanical issue.

5) Dirty interior

If dust builds up within the inner workings of the furnace unit, this can cause multiple components to not work correctly, such as the blower motor and furnace coils, which will not transfer air effectively if they are covered with debris. The furnace overheats because of blockages and/or faulty gears that will put stress on the system.

6) Short cycling

If there is a problem with the heat exchanger or air flow, this can cause short cycling. Short cycling occurs when your furnace is powering on and off in very short bursts rather than running a full cycle. This happens because the high-limit switch begins to control the furnace rather than the thermostat and stresses the workings of the unit.

7) Service life is ending

If a furnace is overheating with no other obvious explanation, it could be due to the age of the system. A furnace is typically good for about twenty years before it starts to break down, so if you are not sure of the exact age of your system, it is a good idea to get an HVAC technician to determine the age for you. And if the furnace is past a certain age where it will not operate stably any more, it is usually a good idea to replace it with a new furnace.

Heating and Cooling Services Options

After identifying the cause of your overheating furnace, what can you do to begin fixing it? What steps can you take to prevent another overheating problem that can cause serious damage to your unit?

Diagnose And Assess

The first step is to hire a professional HVAC contractor to assess all of your HVAC requirements and begin looking for the best solution for your home heating system. There are basic tasks you can handle yourself, like air filter and duct cleaning, but with an HVAC contractor, you can be sure the job is being done correctly and safely. An HVAC technician will be able to safely find any problem within the furnace’s internal components and deal with things like electrical wiring and gas lines.

Repair And Replace

John Owens Services is a professional HVAC company that can provide you with top-of-the-line services for heating and air conditioning. We can fix or replace any overheating furnaces in a safe and timely manner, so you can be assured the issue is taken care of. If your furnace is overheating, we will send in an experienced technician who can locate the problem within your HVAC unit with the proper tools and have your furnace operating like new again in no time.

Depending on the problem with your furnace, there will be options to either repair or replace it. If your furnace is newer than the average twenty-year lifespan, it will most likely be worth investing in repair options. But if it is older, the repair costs might be so frequent that they will outweigh the cost of a replacement. John Owens can provide you with estimates on every option available to you with our competitive prices, so you can decide what will be most cost-effective for you regarding your heating system. Our furnace repair services will allow us to fix up your faulty system or provide you with a new furnace.


One of the best prevention techniques for making sure your furnace does not frequently overheat is to perform regular maintenance on the unit. Annual furnace maintenance, done either by yourself or a professional, can prolong the life of your furnace by years and prevent expensive HVAC repairs in the future. This includes things like duct cleaning, keeping up on the air filter, and making sure things like the blower fan blades are not covered in grime or debris. Most of this should be done right when the heating season is about to begin, since a lot can happen to HVAC systems when they are not in use for a period of time, and much of it can be done yourself. But having regular tune-ups done by a professional technician can always be extremely beneficial.

From Air Filter To Air Handler, John Owens Has You Covered

Whether it is a bad circuit breaker, dust in the thermostat, restricted airflow, or simply an old furnace, there is always an explanation and a fix that an HVAC technician will be able to find. Aside from not getting proper airflow to your home and not having an adequate amount of heat in your house, a furnace that is internally overheating is dangerous to your HVAC system and to your home. Call a professional if you question the safety of your system.

Need Help?

We’re open Monday – Friday 7:30am – 5:30pm, call today or schedule online now!

Serving Marin & Sonoma Counties

Good plumbing, heating, and air conditioning systems are vital in every North California home. John Owens Services, Inc. is proud to be the expert plumbing company you can count on

The John Owens Way

Our philosophy is simple, we always want to maintain equipment to give it the longest life possible. Next, we want to focus on repairing when something goes wrong. Then only as the last choice, we replace equipment when needed. That’s the John Owens Way.

San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464



Regular maintenance keeps your home’s systems running well all year long. We’ll help you gain efficiency and save money.



When something breaks down, our team will get to you fast. We’ll find the problem and fix it to get you back to normal.



When it’s time to replace something in your home, we’ll help you get a top quality product that matches your specific needs.
San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464