Furnace Not Working? Troubleshooting Before You Call

When is a furnace problem an emergency?

In either case, do not try to restart the furnace. Have it checked before it runs again.

Safe checks to try first

1. Thermostat. Make sure it is set to Heat and the setpoint is above the room temperature. Replace the batteries if the screen is blank.
2. Furnace power switch. Most furnaces have a switch near the unit that looks like a light switch. Make sure it is on.
3. Breaker. Check the breaker for the furnace. Reset a tripped breaker once. If it trips again, leave it off and call.
4. Furnace door. Many furnaces will not run unless the front panel is fully closed, because it presses a safety switch.
5. Air filter. A badly clogged filter can make the furnace overheat and shut itself off. Replace it if it is dirty.
6. Condensate drain. High-efficiency furnaces drain water. A clogged drain line or a failed condensate pump can stop the furnace.
7. Status light. Many furnaces have a small light that blinks a code. Note the pattern before you call. It helps with diagnosis.

What not to do

• Do not remove burner or electrical covers
• Do not keep resetting a furnace that shuts off again and again
• Do not try to relight or force a gas valve
• Do not run a furnace with a cracked or disconnected vent pipe

When to call for furnace repair

Call if the checks above do not bring the heat back, if the furnace short-cycles, if you hear banging, rattling or squealing, or if the burner flame looks yellow or flickers instead of burning steady and blue.

Jordan diagnoses the furnace and tells you plainly whether it needs a furnace repair or whether replacement is worth comparing. A yearly furnace tune-up checks burners, ignition and safety controls before the cold weather.