Check These Before Calling (Takes 5 Minutes)
- Check the thermostat. Set it to HEAT, set the temperature above current room temperature, and replace batteries if needed.
- Check the circuit breaker. Look for a tripped breaker labeled Furnace, HVAC, or Air Handler. Gas furnaces still need electricity to run.
- Check the air filter. A clogged filter causes overheating and safety shutoff. Replace it and wait 30 minutes before trying again.
- Check the furnace switch. There's usually a wall switch near the furnace that looks like a light switch. Make sure it's ON.
- Check the gas supply. Make sure other gas appliances (stove, water heater) are working. If not, the gas may be off — call your gas company before the HVAC contractor.
Common Causes of Furnace Failure
- Failed igniter: Most common reason a modern furnace won't light. A $150–$300 repair.
- Dirty flame sensor: The sensor shuts the furnace off if it can't detect a flame. Cleaning or replacing it runs $100–$250.
- Blower motor failure: The furnace lights but no air comes out. $200–$500 repair.
- Cracked heat exchanger: A serious safety issue — carbon monoxide can leak into your home. Requires immediate shutdown and typically a full furnace replacement.
- Control board failure: The "brain" of the furnace. $200–$600 to replace.
If you smell gas, leave the house immediately and call your gas company. Do not operate any electrical switches.
Full cost guide: Furnace Repair Cost Guide