Furnace Not Igniting Burners

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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

If your furnace won't ignite burners, first check the power and gas supply. Then inspect the ignition system and flame sensor. Replace faulty parts if needed.

Confirm the symptom

Furnace fan runs but no heat
No clicking or ignition sound when starting
Burners do not light even after thermostat call for heat
Furnace makes a clicking sound but no flame appears
Thermostat is set correctly but furnace does not ignite

Tools and prep

Screwdrivers (flathead and Phillips)
Multimeter for voltage checks
Flashlight for visual inspection
Gas leak detector or soapy water
Safety goggles and gloves
Owner's manual for furnace model

Step-by-step troubleshooting

Check Power Supply
Do: Verify the furnace is receiving power. Check the circuit breaker or fuse box.
Observe: Breaker is tripped or fuse is blown.
Means: Power interruption caused the issue.
Next: Reset the breaker or replace the fuse and try starting the furnace again.
Verify Gas Supply
Do: Check the gas valve is fully open and there are no gas supply line issues.
Observe: Gas valve is closed or there is a gas leak.
Means: Lack of gas prevents ignition.
Next: Open the gas valve fully and check for leaks. If a leak is found, turn off the gas and call a professional.
Inspect Ignition System
Do: Look at the ignition system (pilot light or electronic igniter) to see if it's working.
Observe: Pilot light is out or igniter is not sparking.
Means: Ignition system failure is preventing burner ignition.
Next: For pilot light, relight it following the manufacturer's instructions. For electronic igniter, proceed to the next step.
Test Igniter and Flame Sensor
Do: Use a multimeter to test the igniter and flame sensor for continuity and proper voltage.
Observe: Igniter is not sparking or flame sensor has no continuity.
Means: Faulty igniter or flame sensor is the issue.
Next: Replace the faulty igniter or flame sensor if testing confirms the issue.
Check for Error Codes
Do: Look at the furnace control panel for any error codes or indicator lights.
Observe: Error code is displayed.
Means: The furnace has detected a specific issue.
Next: Refer to the owner's manual to interpret the error code and take appropriate action.
Inspect Burner Tubes
Do: Visually inspect the burner tubes for dirt, debris, or blockages.
Observe: Burner tubes are clogged or dirty.
Means: Blocked burners prevent proper gas flow and ignition.
Next: Clean the burner tubes with a brush and compressed air, then attempt to relight the furnace.
Test Gas Valve
Do: Use a multimeter to test the gas valve for proper voltage and operation.
Observe: Gas valve is not receiving power or is faulty.
Means: Gas valve failure prevents gas from reaching the burners.
Next: Replace the gas valve if it's faulty or not receiving power.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Tripped Circuit Breaker or Blown Fuse Power interruption stops the furnace from operating.	Common	Easy	Fuse or circuit breaker
Closed Gas Valve or Gas Leak No gas supply to the burners prevents ignition.	Common	Easy	Gas valve
Faulty Igniter or Pilot Light Ignition system failure prevents burner lighting.	Common	Easy–Medium	Igniter or pilot assembly
Dirty or Clogged Burner Tubes Blocked burners prevent proper gas flow and combustion.	Sometimes	Easy	Burner cleaning kit
Faulty Flame Sensor Flame sensor not detecting flame causes the furnace to shut down.	Sometimes	Medium	Flame sensor
Failed Gas Valve Gas valve not opening to allow gas flow to burners.	Sometimes	Hard	Gas valve
Thermostat Issues Incorrect thermostat settings or wiring prevent furnace activation.	Rare	Easy	Thermostat
Control Board Failure Malfunctioning control board prevents proper operation of the furnace.	Rare	Hard	Control board

Parts matching

Common parts needed for a furnace not igniting burners include:

Igniter or pilot assembly
Flame sensor
Gas valve
Circuit breaker or fuse
Burner cleaning kit
Thermostat

Always refer to your furnace's owner's manual to ensure you're using the correct replacement parts for your specific model.

When to call a professional

Gas smell or suspected gas leak
Furnace produces unusual noises or error codes not listed
You're unsure about electrical testing or gas system repairs
Furnace still doesn't ignite after replacing suspected parts
Carbon monoxide detector is sounding or you suspect CO leak
Furnace is older than 15 years and has recurring issues

FAQ

Why is my furnace making a clicking sound but not igniting?

A clicking sound usually indicates the igniter is trying to spark but may be faulty, or the gas valve is not opening. Check the igniter and gas valve for issues.

Can a dirty flame sensor prevent the furnace from igniting?

Yes, a dirty or faulty flame sensor can prevent the furnace from detecting a flame and will shut down the system for safety. Clean or replace the sensor to resolve the issue.

How often should I clean the burner tubes?

Burner tubes should be cleaned at least once a year during routine maintenance to prevent clogs and ensure proper gas flow.

Is it safe to relight a pilot light myself?

Yes, it's generally safe to relight a pilot light if you follow the manufacturer's instructions. If you smell gas or are unsure, call a professional.

What should I do if I smell gas near the furnace?

Immediately turn off the gas supply, open windows, and avoid any sparks. Evacuate the area and call a gas company or emergency services.