If your furnace blower fan is not working, the fan motor is likely defective. Alternatively, you may have a wiring issue. These two are the most common reasons why the furnace blower may refuse to turn. However, it doesn’t mean that you should limit your troubleshooting to the two areas.
For instance, sometimes, the furnace can encounter a problem at the circuit board that causes the fan to stop. Or it could be the fan limit switch.
Let’s discuss the most common reasons in greater detail, so you know what to do when your furnace blower suddenly stops.
What’s the Furnace Fan?
The furnace fan (or blower motor) is an electrical system responsible for blowing and circulating warm air from the furnace into and throughout your rooms/home.
It is typically located near the base of the furnace in the blower chamber and resembles a hamster wheel. You may need to remove two access panels to access it.
Blower motors come in different sizes depending on the size of the furnace. However, most furnaces have one horsepower fan or less. Most fans also rotate at around 1,200 revolutions per minute (RPM), though others are slower and others faster.
How the Furnace Fan Works
Furnace fans kick in after your burners come alive. This usually follows a call for heating by the thermostat. Once the furnace begins to produce warm air, the blower motor engages.
Powered by electricity from the control board (not the home’s main supply), the motor begins to rotate, creating air motion within the blower chamber. This motion helps force the warm air into your ductwork.
Additionally, the motion helps to generate air circulation in your rooms which is necessary to push cold air back into the furnace.
The speed at which it pushes air out of the ducts depends on the type of fan and the size of the furnace. Single-speed fans are either off or running at full speed – there’s no in-between. Meanwhile, dual-stage fans can run at full capacity or half capacity.
Alternatively, modern furnaces use variable-speed fans that can operate at any level between 40% and 100%. Better still, they adjust automatically. So the fan will run faster, say at 80%, when you need more heating, and slower, say, at 45% when the room is at the thermostat setting.
The blower motor keeps running normally as long as everything is fine, only stopping when you switch off the furnace. Indeed, it will keep blowing even when the furnace cycles off to circulate warm air throughout the house. So, something must be wrong if it stops suddenly.
How Can You Tell That Your Furnace Fan is Bad?
It’s easy to tell when you have a bad furnace fan. The following are a few common clues to listen/watch out for;
- The furnace is dead quiet: We all desire a quiet furnace. However, that’s never possible because of the blower motor, which generates a low hum when running. If the humming stops suddenly, the motor might have stropped turning.
- Strange furnaces: Another telltale sign of a defective blower motor is strange furnace noises. A screeching, rattling, or clanking noise often points to a broken motor. Maybe one of the components has come off, or the belt is worn out.
- Poor or no airflow from supply vents: You also probably have a bad furnace blower if your home seems to be getting colder and colder because of poor or no airflow from the supply vent. Try placing the back of your hand close (but not too close) to the vent to feel the airflow. If it’s feeble or non-existent, your blower fan could be bad. The noises are most pronounced when starting or shutting the furnace.
- Skyrocketing heating bills: If the blower is dirty, clogged, or compromised in another way, it may run harder and longer to keep up with heating demands. Since it draws power from the furnace’s control board, the longer, harder operation may increase heating bills.
- Overheating signs: Finally, you should also watch out for signs of internal overheating. For instance, a burning smell can be a sign of blower motor overheating. The furnace may even shut down if the overheating goes on for too long unchecked.
Reasons Why Your Furnace Fan Isn’t Working and How to Fix Each
Unfortunately, it’s not very easy to pinpoint what could be wrong when your furnace fan isn’t working. But, the most common reasons are as follows;
1. Thermostat Setting/Issues
The thermostat is the first thing you need to check immediately you find out that your furnace fan isn’t working. Why? Because the thermostat essentially controls the operation of the blower motor. It indirectly tells it when to run and when to stop.
The fan typically stays off until the thermostat calls for heating. It will stay off as long as there’s no call for heating.
Solution: You need to find out and fix the reason why your thermostat isn’t calling for heating. Is it broken? Is it a wrong setting?
2. Electrical Power Issues
The fan could also be off because it’s not getting power from the circuit board or because one of the electrical circuit relays is open. For instance, loose or disconnected wires can keep the fan off. Or you could be looking at a blown fuse.
Solution: Check whether the furnace is displaying error codes that might point to open switches. Additionally, make sure the fan is getting power by probing the wiring and verifying that you don’t have any blown fuses within the furnace.
3. Is the Drain Pan Full?
More than 90% of furnaces in use today are condensing furnaces that condense moisture in a special drain pan to ensure maximum heating efficiency. The condensate is held in a drain pan and drains out automatically.
However, if there’s a blockage that keeps the water from draining, a condensate pan switches lockout may ensue and automatically discontinue the heating process.
Solution: Most furnaces will use onboard error codes to alert you about condensate pan switch lockout. Alternatively, you can manually check and drain the condensate pan. Then, restart the furnace when you’re done to see if the problem is gone.
4. Defective Heat-Activated Fan Switch
Some older furnaces use heat-activated fans, which only come on once temperatures within the furnace reach a pre-defined level. The burner flame must be ON and the heating chamber warm for these types of fans to work. If the flame becomes weak or goes off, the fan will stop.
Solution: Check whether your furnace uses a heat-activated blower fan. If so, check whether the fan is switched “ON” on the thermostat. If so, it should come on automatically when the burners are lit. Otherwise, the heat0activated switch is likely bad and needs repair or replacement.
5. Damaged Blower Motor
Finally, if the furnace fan is not working, the fan itself could be damaged or defective. This is especially true if you can hear strange sounds from your furnace. The strange noises could point to one of the following issues;
Since furnace blowers need more power than the circuit board can provide during startup, they typically use capacitors to hold startup energy. Now, imagine if the capacitor is bad or dying! It wouldn’t provide enough juice to kickstart the fan. Thus, the fan will remain off. It may attempt to start but fail midway.
Solution: You need to test and, where necessary, replace the capacitor. Typically, if you can rotate the fan freely, but the same fan cannot rotate on its own when you power on the furnace, the capacitor is dead and needs replacing.
Older furnaces use a belt-drive blower motor. If the belt is old and loose, it may rotate without necessarily rotating the motor.
Solution: Find an HVAC professional to diagnose and repair or replace the belt.
The motor is dead
Finally, you may also be dealing with a dead motor. A bad motor cannot work no matter how hard you try. You won’t even get the humming sound often heard when you have a bad blower capacitor.
Solution: Find an HVAC technician to test the motor to prove that it’s dead. If so, replace it without further delay as you cannot resurrect a bad blower motor.
How to Reset a Furnace Fan
You can always attempt to reset the furnace blower fan before you replace it. It’s a simple process that takes two minutes at most.
- Switch off the furnace at the breaker
- Remove the front panel to access the fan
- Locate the small round component on top of the furnace blower box. Can you see the red or white button at the center? This is the reset switch.
- Press and hold the switch for 2-3 seconds, then release it.
- Now put the front panel back, turn on the furnace’s power, and restart the unit. If it works, you’ve just reset the furnace.
How Much Does It Cost to Replace a Furnace Fan?
If resetting doesn’t work and the problem seems beyond repair, replacement is the only other solution. The cost to replace the blower motor is $200 to over $2,000, depending on whether you do it yourself or hire a professional. However, it costs around $450 on average.
Now you know potential reasons why your furnace fan isn’t working and how to troubleshoot and solve the problem. Remember that fixing the issue early is critical as left unchecked, furnace blower motor issues can transform into more serious problems.