Many homeowners get frustrated with their furnace when it won’t turn on. Others become puzzled when their unit won’t stop running.

Yes, it is possible for your HVAC system’s blower fan to run continuously even when you expect it to shut off. There are logical reasons behind this phenomenon, and you can often fix the problem yourself with some simple troubleshooting.

If the blower fan of your furnace refuses to quit running, do the following:

Check the Thermostat

Sometimes, the fan runs non-stop because the thermostat forces it to. This device is responsible for tracking the air temperature in the room and dictating when heat is needed to regulate the space’s indoor climate.

To rule out the possibility that your thermostat is defective, change its temperature setting. Make sure that it’s set below the room temperature to keep it from powering on the furnace. If the fan still runs after doing this, your thermostat is not the problem.

Next, make sure your thermostat’s fan control is on AUTO. If it’s set to ON, that’s probably the reason why you can still hear your furnace operating. Switch it to OFF or AUTO, and your heating unit should become quiet.

Look for the Fan Limit Control Switch

If your furnace is still loud despite making sure that the fan control is set to AUTO or OFF, go to the fan blower unit itself. It may have a manual fan limit switch that can override your thermostat.

This control usually comes in the form of a white pull-push switch. Read the label that tells which is which. If the position of the switch is not on AUTO, flip it the other way, and that should do the trick.

When All Else Fails, Call an Experienced San Francisco HVAC Technician

When all of your troubleshooting efforts prove to be fruitless, contact McMaster Heating and Air Conditioning to have a qualified HVAC technician investigate further. Call us at (949) 481-7995 or fill out this form to request service and unravel the mystery behind your continuously running furnace.