Fan Only Mode Not Working On Furnace – What Could Be Wrong?

Has your furnace blower motor stopped working suddenly? You can see and hear it turn on but it won't start. We delved deep into this problem to determine what is causing it and here's what we found.

There could be a number of reasons why your furnace's fan-only mode won’t work. These include:

  • Blown or tripped circuit breaker: The circuit can overload, causing the wires to blow.
  • Incorrect thermostat setting: The wrong temperature prevents the blower motor from starting when it needs to.
  • Clogged filters and vents: This results in a lack of airflow and the blower motor won’t run since there’s no air to circulate in the first place.
  • Damaged blower motor belt: The blower motor wheel pulley won’t power up if the belt is defective.
  • Bad capacitor: If the capacitator goes out, the fan won’t turn on as this part is responsible for supplying the electrical current.

So how do you determine which of these reasons is the culprit and how do you fix the problem? In this post, we’ll show you how you can fix it yourself before you call an HVAC contractor. 

New clean filter is being inserted into a home furnace, Fan Only Mode Not Working On Furnace - What Could Be Wrong?

What Happens When The Fan-Only Mode Stops Working?

Service Man Working on Furnace

The fan-only mode allows you to cycle the air at home without heating or cooling the air. If it stopped working, you lose the ability to maintain the air at room temperature.

Why The Fan-Only Mode Isn’t Working And How To Fix It

Here’s a breakdown of why the fan-only mode won’t work and how to fix it: 

1. Blown Or Tripped Circuit Breaker

If the furnace blower has no power, the circuit breaker might have overloaded or tripped. You'll need to inspect if the cables are in good condition. If the wires look fine, try to unplug them, then plug them back in. You may switch the fuse box on and off as well.

2. Incorrect Thermostat Setting

If the fan does turn on, the next thing to do is check is the thermostat.

As mentioned above, the incorrect thermostat setting prevents the fan from running. By default, it’s set to “Auto” and “68°F”. Switch it to “On," then increase the temperature by three to five degrees. The furnace blower should work after doing this. If it doesn’t, proceed to the steps below. 

3. Clogged Vents And Filters

Vents and filters regulate the air. If they get clogged, the airflow becomes restricted. So make sure that they have no dust build-up. Wipe off any dirt with a rag.

4. Damaged Blower Motor Belt

This is the part that powers up the blower motor by connecting the wheel pulleys. To inspect the motor belt, turn off the circuit breaker, and check for any signs of damage. If it’s already worn out, you might need to replace it. 

5. Bad Capacitator

This part stores electrical current to run the blower motor continuously. A good indicator that the problem is the capacitor is if the blower motor hums but doesn’t do anything.

If this is the issue, don’t attempt to fix it yourself as there's a lot of risk in doing so due to the high voltage involved. It’s best to leave the job to a professional technician.

Resetting the Blower Motor

Exhaust fan of an air conditioner

If none of the above is the problem, sometimes resetting the blower motor does the trick. Here’s how to do this: 

  1. Turn the furnace off. 
  2. Take off the blower motor cover to unscrew the front. 
  3. Allow the blower to cool until it’s safe to touch. 
  4. Look for the reset button. It’s located at the back of the heater. Just push the button in and it should pop. If it doesn’t, it means the blower motor has gone out already. 

Fan Won't Run On Auto Mode

In some cases, the motor runs on manual but not on auto mode. Below are the possible reasons for this: 

Lack of Heat

The heat source might have stopped working, keeping the burner from turning on. 

Broken Temperature Sensor

There are cases where the furnace heat source works but the switch that automatically turns on the fan doesn’t.

Defective Control Board

This controls the blower assembly. If it’s worn out, the fan becomes inoperable. 

Signs That Your Furnace Blower Needs To Be Replaced 

Technician servicing heating boiler

Low Airflow Out of the Vent

This means that the fan has difficulty pushing the air into the ducts. It's also the first indication of a damaged blower motor.

Absence of Airflow

The fan might have reached the stage where it’s completely unusable. However, this can also be due to a faulty thermostat or a bad battery. 

Higher Utility Bill

The blower motor consumes a lot of energy. If it works harder than usual, you will notice a significant increase in your energy bill.  

Unusual Sounds

Squeaking sounds indicate a broken motor belt or bearing, while a loud banging noise usually means a part breaks away from the main component. Most of the time, the solution for this is a complete replacement. 


As the furnace blower ages, it becomes harder for it to achieve your desired temperature, leading to overheating. 

Replacing Your Furnace Blower Motor

Closeup of heater exhaust fan inside of furnace.

If your blower motor needs to be replaced, you have to consider a couple of things such as the horsepower, speed, voltage, size of the capacitor, and more.

Make sure to talk to your HVAC contractor if you are unsure which model best suits your furnace,. They can assess your HVAC system to determine which blower fits your unit.

Check out this blower motor on Amazon.

How Much Does It Cost To Replace A Furnace Blower?

A new furnace blower motor can cost around $400 to $600. This price already includes the labor. However, you can also replace the blower motor yourself. It’s fairly easy to do as it is designed in a way that allows you to remove and put it back easily. 

How Long Should You Run Your Furnace Fan?

You can run your furnace fan 24/ 7 without having to worry about it breaking down since it's specifically designed to run continuously. Running it all day actually comes with benefits such as improved airflow, lower energy bills, and quality indoor air. 

When Should You Not Run The Furnace Blower?

Don’t run the fan in the middle of summer if you have ductwork in the attic. This is because the temperature can reach up to 140°F in this season regardless of whether it's well-insulated. Running the fan with the air conditioner only contributes to excessive heat which can spread throughout the house.  

You should also not run the fan if there’s a leak in the ductwork; it can compromise the airflow. Make sure that it’s sealed and airtight.

How Long Does A Furnace Blower Usually Last?

Most manufacturers claim that their products have a life expectancy of 20 years, but blower motors usually last for only up to 10 years. With proper maintenance, you can increase its lifespan by two to three years. 

Ways To Maintain Your Furnace

Clean The Access Area And Blower Compartment Periodically

This part that houses the blower assembly is prone to dust buildup. To clean it, open the access area and check for debris and dust. Use a vacuum to suck them out. Then brush off the residue on the mechanical parts. 

While cleaning, check for any loose wires. Secure them in place with a screwdriver or wrench. Be careful with this step to avoid accidents. Lastly, check the burner for corrosion. 

Change The Filter

Male hands are installing a furnace air filter.

As a general rule, you should replace the filter every month. But some filters last for three months, depending on the quality. Failure to replace the filter regularly can shorten the blower motor's lifespan.

Lubricate The Blower Motor

If the motor has shaft ports, they need to be lubricated on a regular basis to function properly. Just place two to three drops of non-detergent motor oil on each port. Avoid overlubricating. After that, check for wear or crack on the motor belt. 

Check Flue Pipes For Leaks

The combustion byproduct such as carbon monoxide can leak into the flue pipe holes, which poses health risks. Make sure that it is venting properly. For the tiny holes, use foil tape to patch them. 

Check out this foil tape on Amazon.

Clean The Air Registers

This grill traps dirt, pet hair, and food particles which restrict airflow. Use a high-powered vacuum to remove obstructions on it. 

Check out this vacuum on Amazon.

Wipe The Thermocouple

Dirt can accumulate on the thermocouple over time, causing problems with the pilot light. It's a good idea to clean it up annually. However, this would require necessary tools as you have to unscrew and remove some components. Unless you know what you are doing, leave the job to professionals. 


close up front side of nozzle burner head for industrial such as furnace or oven for manufacturing

There are a couple of reasons why a blower motor stops working, such as a tripped circuit breaker, incorrect thermostat setting, clogged filters and vents, damaged blower motor belt, and bad capacitator.

It’s important to determine the source of the problem so you can use the appropriate solution. If you need assistance, don’t hesitate to call an HVAC technician. 

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