Furnace Not Working After Power Outage

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Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

After a power outage, reset your furnace by turning it off at the thermostat and circuit breaker for 30 seconds, then restore power. Check for error codes and ensure the gas valve is open. If it still doesn't start, contact a professional.

Confirm the symptom

Furnace was working before a power outage
Power has been restored to the house
Furnace does not start or blow heat
Thermostat shows power but no response
No unusual smells or noises from the furnace

Tools and prep

Thermostat
Circuit breaker panel access
Flashlight
Screwdriver (if needed for panel)
Gas valve key (if applicable)
Safety gloves and glasses

Step-by-step troubleshooting

Check Thermostat Settings
Do: Ensure the thermostat is set to 'Heat' and the temperature is higher than the room temperature.
Observe: Thermostat displays correct settings and power.
Means: Thermostat is functioning and properly configured.
Next: Reset the furnace.
Reset the Furnace
Do: Turn the thermostat off, then turn off the furnace's circuit breaker for 30 seconds. Restore power and try turning the furnace on again.
Observe: Furnace may restart and begin heating.
Means: The furnace may have needed a power reset after the outage.
Next: Check for error codes or lights.
Check for Error Codes
Do: Look at the furnace control panel or blower compartment for flashing lights or error codes.
Observe: Error code or light pattern is visible.
Means: The furnace has a specific issue that needs addressing.
Next: Consult the furnace manual for the error code meaning.
Verify Gas Valve is Open
Do: Locate the gas valve near the furnace and ensure it is fully open (handle parallel to the pipe).
Observe: Gas valve handle is aligned with the pipe.
Means: Gas supply is available to the furnace.
Next: Check the pilot light or ignition system.
Check Pilot Light or Ignition System
Do: For gas furnaces, check if the pilot light is lit. For electronic ignition, ensure the igniter is functioning.
Observe: Pilot light is lit or igniter glows and ignites the burner.
Means: Ignition system is operational.
Next: If pilot is out, follow manufacturer instructions to relight it.
Inspect Air Filter
Do: Remove and inspect the air filter for blockage or dirt.
Observe: Air filter is clean or dirty.
Means: A dirty filter can restrict airflow and prevent proper operation.
Next: Replace the filter if it's dirty.
Check Blower Motor and Fan
Do: Listen for the blower motor to engage and the fan to start when the furnace is on.
Observe: Blower motor hums or fan spins.
Means: Blower motor and fan are operational.
Next: If no sound, check for tripped motor or electrical issues.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Power not fully restored to furnace The circuit breaker may have tripped or the power may not have fully returned.	Common	Easy	None
Thermostat settings incorrect The thermostat may have reset during the outage or be set to 'Off' or 'Cool'.	Common	Easy	None
Gas valve closed The gas valve may have shut off during the outage or was manually closed.	Sometimes	Easy	None
Dirty air filter A clogged air filter restricts airflow and can prevent the furnace from starting.	Common	Easy	Air Filter
Pilot light out The pilot light may have gone out during the outage, especially in older furnaces.	Sometimes	Easy–Medium	None
Ignition system failure Electronic ignition systems can fail after a power interruption.	Sometimes	Medium	Igniter
Blower motor or fan issue The blower motor may have failed or the fan may be obstructed.	Rare	Hard	Blower Motor
Main control board failure A power surge during the outage may have damaged the control board.	Rare	Hard	Control Board

Parts matching

If your troubleshooting shows a part needs replacement, here's how to match it:

Check the furnace model number on the data plate for exact part compatibility.
Take the old part to the store for an exact match.
Use the furnace manual to identify correct part numbers.
Search online using your furnace's model and part name.
Consult a professional for complex parts like control boards.

Always purchase parts from reputable HVAC suppliers to ensure quality and compatibility.

When to call a professional

Furnace still doesn't work after following all troubleshooting steps
You smell gas or hear unusual noises
Error codes indicate a complex issue
You suspect electrical or gas line damage
You're unsure about handling gas or electrical components

FAQ

Why won't my furnace start after a power outage?

It may need a power reset, the gas valve might be closed, or there could be an issue with the ignition system or control board.

How do I reset my furnace after a power outage?

Turn off the thermostat, then turn off the furnace's circuit breaker for 30 seconds. Restore power and try turning the furnace on again.

Can a dirty air filter cause my furnace to stop working?

Yes, a very dirty air filter can restrict airflow and prevent the furnace from starting or operating safely.

What should I do if I smell gas after a power outage?

Immediately shut off the gas valve, open windows, and call a professional HVAC technician or gas company.

How can I tell if my furnace's pilot light is out?

Look through the access panel or follow the manual's instructions to check the pilot light. If it's out, follow the manufacturer's relighting procedure.