Why Isn't My Furnace Heating?

A common furnace repair issue homeowners face in the winter is their furnace not heating. A furnace not heating can be caused by a few different issues. This problem may be corrected by some quick troubleshooting, or may require the assistance of a furnace repair technician.

Troubleshooting a furnace not heating

A furnace not heating may be caused because the thermostat is not telling the furnace to fire up! These troubleshooting steps may help if the thermostat settings are to blame:

• Check batteries and power source to ensure the thermostat is powered.
• Make sure heat mode is selected.
• Set the temperature a few degrees higher than the current room temperature.

If the furnace doesn’t have power, it will not turn on, preventing heating.

• Check the furnace’s power source at the breaker or fuse box. Reset breakers and change out fuses if needed.
• Check the on/off switch near the furnace or air handler to make sure it is set to on.

If the furnace does not have fuel, it will not create heat.

• Make sure the gas supply valve to the furnace has not been turned off.
• If you have an oil or propane furnace, make sure there is fuel available in the tank for heating.

The furnace may not be heating because the motor has been overloaded, requiring reset.

• Press the reset button, located on the front or side of your unit.

Issues causing furnace not heating

A faulty pilot light can be the cause of a furnace not heating in an older system. If the pilot light will not stay lit, several issues could be to blame. A furnace repair technician will diagnose the source of the issue and make needed repairs, which could be replacing the thermocouple or safety cutoff valve, cleaning the pilot light’s orifice, or adjusting the flame.

If the flame sensor is dirty, the furnace will not function because it is protecting against burning heating fuel unsafely. The flame sensor may require cleaning or readjustment.