Furnace Inducer Troubleshooting – Here’s What to Do

Are you having trouble with your furnace’s inducer fan?

Maybe it’s just rattling a little bit. Or maybe it’s not starting up at all. 

Either way, issues with a furnace inducer fan will prevent your furnace from running– leaving your home in the cold.

In this article, I’ll cover ALL of the possible issues that your furnace’s inducer fan can experience. From bad bearings, no power, and even what to do when it keeps turning on and off.

Let’s get started!

Inducer fan is vibrating

If you hear a rattling or vibrating noise coming from your furnace’s inducer, then it’s usually not too much of a cause for alarm.

In most cases, the inducer fan housing is a little bit loose and it just needs to be tightened back down.

To fix a vibrating inducer fan, follow these steps:

  1. Power down your furnace. Turn off the power disconnect to your furnace so it won’t turn on while you’re taking it apart.

  2. Remove the access panels to your furnace. Specifically, you need to remove the panel that gains you access to the inducer fan assembly.

  3. Turn your furnace back on. Turn power back on to your furnace and set your thermostat to heat mode. 

  4. Look (and listen!) for the source of the vibrations. The idea is to watch your inducer fan turn on so you can identify what’s causing the vibrations. When working inside your furnace, be careful since the inducer fan can get extremely hot, especially if it’s an 80% furnace. Here are a few tips:

    1. Press on the inducer fan housing to see if that stops the rattling. 

    2. Other times, it may be a screw on the inducer fan assembly that needs to be tightened up.

    3. If neither of the above works, then you can try placing a shim between the inducer fan assembly and the furnace cabinet to make the vibrations stop. Use something metal such as a screw, nail, or sheet metal. Do not use wood or plastic for a shim because those things can burn or melt.

    4. Debris inside of the inducer motor housing could also be the source of the vibration. I discuss debris inside the inducer below.

    5. The worst-case scenario is bad bearings in your inducer motor. I discuss bad inducer motor bearings below.

  5. Fix the source of the vibration. Depending on the source of the vibration that you identified in the step above, you may need to do something as simple as tighten up a screw. Or something more complicated such as taking apart your inducer and cleaning its insides.

  6. Put your furnace back together. After you’ve removed the vibrations from the inducer, it’s time to reassemble your furnace. Put everything back where it was, and close up its access panels.

Stuck inducer fan motor

A stuck inducer motor is another common inducer motor issue.

If your inducer motor is stuck, it is sometimes just a simple fix. Other times, you’ll need to replace the entire inducer motor assembly. 

It just depends on what’s causing the motor to be stuck.

To fix a stuck inducer motor, follow these steps:

  1. Power down your furnace. Turn off the power disconnect to your furnace so it won’t turn on while you’re taking it apart.

  2. Remove the access panels to your furnace. Specifically, you need to remove the panel that gains you access to the inducer fan assembly.

  3. Find the inducer motor and give it a spin. Most inducers will have a piece on the back of the motor that you can grip and turn by hand. Some inducers will have some fan blades recessed into the motor. For those, use a screwdriver to turn the fan blades.

    When spinning the inducer fan manually, there will be one of three outcomes:

    1. If the inducer motor turns freely, then there is likely an electrical power issue going on with your inducer motor. I cover inducer motor power testing below.

    2. If the inducer motor has a lot of resistance or if there is grinding when you try to turn it, then there is debris in the inducer. Or the inducer motor’s bearings are bad.

    3. If the inducer motor is stuck at first, but then spins freely, then it may have been just a temporary “binding” of the motor. This usually happens during the first time you start up your furnace in the fall. The inducer motor can sometimes get a little stuck since it hasn’t run for a few months.

  4. Fix the stuck inducer motor. Depending on the cause of the stuck inducer motor, you will need to fix it accordingly.

    I’ll go over what you should do in each scenario below.

Debris inside inducer fan motor assembly

Sometimes leaves or bird’s nests can find their way down your exhaust vent and into your inducer fan housing. 

If this is the case, then you’ll need to remove the debris from the fan so it can spin freely again.

The process for removing debris from your inducer fan depends on the type of inducer that you have.

Some inducers are easy to take apart and clean. For other inducers, the only option is a replacement.

Inducer fan motor bearings are bad

If your inducer motor is still grinding after its fan is free of debris, then its motor bearings are bad.

The bearings are responsible for keeping the inducer motor spinning smoothly as it rotates.

Unfortunately, motor bearings are not something that you can repair. So you’ll need to replace the inducer fan assembly if the motor bearings are bad.

Inducer fan motor electrical and power issues

If your inducer motor spins freely but won’t turn on, then it’s likely an electrical or power issue.

The first thing that you need to check is if your inducer motor is getting power from the furnace’s control board.

Follow these steps to figure out if your inducer motor is getting power:

  1. Use a multimeter on the voltage setting to test power going to the inducer motor. Probe the hot (black wire) and neutral (white wire). You should get 120VAC when furnace is in heat mode.

  2. If you do not have 120VAC going to the inducer motor, then you need to check the furnace’s control board:

    1. Check if the board is getting power. Use your multimeter to test for 120VAC going into the control board. The exact terminals that you need to probe will vary from furnace to furnace.

      One way to figure out which terminals to check is to look where the line side (white and black wires) of the transformer connect to the control board. If your control board is not getting 120VAC then you need to make sure that power is on to your furnace and there are no tripped circuit breakers.

    2. Use your multimeter to test between the R and C terminals on your control board. You should get 24VAC across these terminals. If you don’t measure 24VAC across the R and C terminals, then there is an issue with the control board or its transformer.

    3. Check if the board is receiving a call for heat. Use your multimeter to test between the W and C terminals on the control board. You should measure 24VAC across these terminals.

      If you aren’t measuring 24VAC across the W and C terminals, then there is an issue with your thermostat since it is not calling for heat. You can always bypass the thermostat by using a wire to jump the W and C terminals to manually put your furnace into heating mode.

  3. If you are measuring a low voltage to your inducer motor, such as 70 or 80VAC, then you need to check the wiring connections between the inducer motor and the control board. If all the wiring connections are good and you are still only getting low voltage going to the inducer motor, then it’s likely that the control board is bad.
Jumping R and W terminals on furnace control board
Jump the R and W terminals on your furnace’s control board to bypass the thermostat

After you’ve checked that your inducer motor is getting power and it’s still not starting, it could be something else.

Here are a few different electrical issues that your inducer motor could have:

Bad inducer fan motor capacitor

The capacitor is responsible for providing the initial “push” to get the motor spinning.

One of the telltale signs that your inducer motor has a bad capacitor is if the motor gets really hot without even starting. This means that power is getting to the inducer motor, but the capacitor is not able to give it that initial jolt of electricity to get the motor started.

If the inducer fan motor capacitor is bad, then it will need to be replaced.

Bad inducer fan motor motor windings

In some cases, extreme temperatures will cause the windings inside the inducer motor to burn out and go bad. 

Sometimes, it will be obvious that the inducer motor is burned out. For instance, if you have the classic “burnt electrical smell” coming from your inducer motor, chances are that the motor is burned out and needs to be replaced.

To test if the inducer motor windings are bad, follow these steps:

  1. Disconnect the inducer motor. Find the wiring harness for the inducer motor and disconnect it. The inducer motor wiring harness is usually white with 3 or 4 wires.

  2. Use a multimeter to test the resistance across the inducer motor. Turn your multimeter on to the resistance or ohms (Ω) mode. Use the two multimeter probes to test the hot (red or black wire) and neutral (white wire) pins on the connector that goes to the inducer motor. There should be between 20-100 ohms of resistance between the hot and neutral wires, depending if the hot wire is for low or high speed.

    If your multimeter reads open line (OL) or a high resistance reading, then your inducer motor windings are bad and the inducer motor assembly will need to be replaced.
Interior of furnace showing inducer fan motor wiring connector
The inducer fan motor connector is usually white and has 3 or 4 wires

Bad furnace control board

If the inducer motor isn’t getting power, then it could be an issue with the furnace control board. The control board is responsible for turning on and providing power to the inducer motor.

For more information on troubleshooting a furnace control board, check out my article on furnace control boards.

Loose inducer fan motor wiring connection

If the inducer motor is only getting partial voltage (such as 70 or 80VAC), then it could be a loose connection.

Another symptom of a loose wiring connection is an inducer fan that keeps turning on and off.

Check all the connectors between the inducer fan motor and the furnace control board to make sure they are tight. 

Sometimes you need to just unplug and then plug back in the inducer motor to restore the connection.

Inducer fan motor won’t stop running

If your inducer fan motor keeps on running all the time, it’s most likely due to a tripped safety such as the high limit switch.

It could also be due to a bad control board that is “stuck” in the on position for running the inducer fan.

The first thing you need to do is turn off the power to the furnace so the inducer fan stops running.

The inducer fan motor is not designed to be running 24/7– if it is, it may damage itself.

Next, you’ll need to start troubleshooting to check what is causing the inducer fan motor to stay running:

Inducer fan motor keeps turning on and off

There are two common causes for an inducer fan that keeps turning on and off:

  1. Loose wiring connection
  2. Pressure switch issue

I already covered loose wiring connections above. So I’ll just go over pressure switch issues here.

Inducer fan pressure switch issues

The pressure switch on an inducer fan is used to check that there is proper airflow out of the furnace’s exhaust. Sufficient airflow is needed to exhaust all of the toxic combustion gases outside of your home.

The inducer’s pressure switch needs to trigger before the furnace will ignite its burners and heat your home.

The most common cause of a pressure switch that’s not triggering is blocked exhaust venting.

You can read my article on blocked furnace exhaust vents here.

The gist of the article is that you need to check for and clear out any debris from your furnace’s exhaust vent to ensure unobstructed airflow.