High Priority Issue
Furnace Won't Turn On?
When your furnace refuses to start, here's what could be wrong and when you need professional help.
Get Same-Day DiagnosisQuick DIY Checklist (Try These First)
Thermostat set to HEAT
Temperature above room temp
Thermostat batteries fresh
Circuit breaker ON
Furnace power switch ON
Gas valve open
Common Causes & Solutions
Thermostat Issues
Low PriorityDIY Fix
Thermostat not set correctly, dead batteries, or malfunctioning.
Solution: Check thermostat is set to HEAT, temperature is above room temp, and replace batteries if needed.
Tripped Circuit Breaker
Low PriorityDIY Fix
The furnace's electrical circuit has tripped.
Solution: Locate your electrical panel and reset the furnace breaker. If it trips again, call a professional.
Furnace Switch Turned Off
Low PriorityDIY Fix
The power switch on or near the furnace is in the OFF position.
Solution: Locate the switch (looks like a light switch) near your furnace and flip it to ON.
Clogged Air Filter
Low PriorityDIY Fix
Severely clogged filter triggered safety shutdown.
Solution: Replace the air filter and try restarting the furnace.
Gas Valve Closed
Medium PriorityDIY Fix
The gas supply to the furnace has been shut off.
Solution: Check that the gas valve handle is parallel to the gas line (open position).
Ignition System Failure
High PriorityCall Pro
Electronic igniter or pilot light has failed.
Solution: Professional diagnosis and repair of ignition components required.
Flame Sensor Malfunction
Medium PriorityCall Pro
Dirty or failing flame sensor prevents ignition sequence.
Solution: Professional cleaning or replacement of flame sensor.
Control Board Failure
High PriorityCall Pro
The furnace's main control board has malfunctioned.
Solution: Professional diagnosis and potential board replacement.
When to Call a Professional
- All DIY checks completed but furnace still won't start
- Circuit breaker keeps tripping
- You smell gas near the furnace
- Error codes displayed on furnace
- Furnace attempts to start but shuts down immediately
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