Furnace Won't Turn On? Troubleshooting Guide
A furnace that won't start leaves you without heat when you need it most. This can be caused by simple issues like thermostat settings or more complex electrical and mechanical problems.
Signs & Symptoms
Possible Causes
- -Thermostat issues (settings, batteries, wiring)
- -Tripped circuit breaker
- -Gas valve closed
- -Pilot light out or igniter failure
- -Safety switch tripped
- -Faulty flame sensor
- -Blower motor failure
- -Control board malfunction
- -Gas supply interrupted
DIY Troubleshooting Steps
Try these steps before calling a professional (unless it's an emergency):
- 1Check thermostat is set to "heat" and above room temp
- 2Replace thermostat batteries
- 3Check and reset circuit breaker
- 4Verify gas valve is in "on" position
- 5Relight pilot light if equipped
- 6Check furnace door is properly closed
- 7Look for error codes on display
When to Call a Professional
- !Smell gas (evacuate, call gas company)
- !Circuit breaker keeps tripping
- !Pilot won't stay lit
- !Error codes displayed
- !DIY steps don't resolve issue
- !Furnace is making unusual sounds
Estimated Repair Costs
Diagnostic: $89-$129
Minor Repair: $150-$350
Major Repair: $400-$1,500
Igniter and sensor repairs are minor. Control board or motor replacement is major.
Prevention Tips
Frequently Asked Questions
Why won't my furnace turn on?
Start with the basics: thermostat settings, batteries, and circuit breaker. If those are fine, common causes include a failed igniter, tripped safety switch, or faulty control board.
How do I read my furnace error codes?
Most modern furnaces have LED lights that flash codes. Check your owner's manual or look for a code guide on the furnace door. Common codes indicate ignition failure, flame sensor issues, or limit switch trips.
Need Help?
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