Troubleshooting a Broken Heater Fan

Check your furnace's on-and-off switch to make sure it is set to “On.” In some cases, the furnace powering your heater — which connects to the blower fan — may have simply been shut off. If your furnace has a fan switch, set it to “On.”

Check the circuit breaker. If the circuit powering your furnace's blower fan has been turned off, the fan won't run. Turn all circuits to the “On” position.

Replace your furnace's filter, as a blocked filter may cause your heater fan to stop blowing. Open the blower compartment door near the unit's bottom; you'll see the current filter. Remove the current filter and put a new one in its place, securing it inside the lips or brackets on the furnace. Note any arrows on the filter, which indicate the proper way to face the filter.

Oil the fan, if your furnace's manual recommends doing so. Open the blower compartment door and apply machine oil to the fan's bearings. Fans with sealed bearings do not need oiling.

Examine the condition of the blower fan's fan belt. Realign the belt if it appears askew or replace it if it feels worn. With an adjustable wrench, loosen the bolts holding the blower motor in place, creating slack in the belt. Straighten the belt or remove it and replace it with a new one. Re-tighten the bolts, but be careful not to make them too tight; you may wear out the blower's bearings.

Contact a repair technician if you notice burn spots around the blower motor, which indicate a control board in need of replacement. Likewise, contact a repair technician if your heater fan makes a grinding noise, which indicates faulty bearings, or if your previous troubleshooting attempts have not restarted your heater's fan.

Allow the heater to run through a complete heating cycle after troubleshooting. A healthy fan runs for about two to three minutes after the burner turns off.