What to Do When a Furnace Blower Fan Won't Start

A repair technician fixing a furnace.

A furnace blower fan is one of the main components in a hot air furnace or home heater system. The blower fan helps to circulate hot air throughout the home. However, it is prone to different kinds of problems. One of the most common issues with a furnace blower fan is the inability to start. Diagnosing the problem correctly can help fix the problem. Here are some probable causes behind this situation and ways to deal with them.

Blower Relay

One of the most common problems with furnace fans is a bad blower relay. The first thing to do is check the relay or voltage from the board. If no voltage is recorded, you will have to replace the board or the relay. If there is a battery, check if it is working properly.

Fan Control

This is another common reason behind faulty blower fans. Check the AFC (automatic fan control) for dust and other accumulation. Adjusting the rise and fall of temperature can also help solve the problem.


Another way to diagnose the problem is by jumping out the thermostat. Turn the power to the furnace off and disconnect the wires from the thermostat. Tie the red and white wires together, and switch the power on. If the furnace starts, the problem is either with the thermostat wire or thermostat. Replace the wire or thermostat to fix the problem.

Your furnace blower fan not starting can have a few causes as you see here. Hopefully, yours is an easy remedy!