Furnace flame sensor proves burner flame so gas can remain on. Related symptoms include burners light then stop, ignition lockout or flame-sense code. Those symptoms do not prove the component failed: record the sequence and exact code before assuming contamination.
What this covers
- gas furnaces
What it does not cover
Differential
Likely causes of “Furnace flame sensor”, and how to tell them apart
- 1
The burners light and shut off because of a dirty sensor
What separates it The flame appears for a few seconds and then goes out, repeating until lockout, and the flame sensor looks coated.
How to confirm Note the sequence and the exact code; cleaning belongs to a qualified technician.
- 2
Gas or air is not reaching the burners properly
What separates it The flame is weak or lifts off the burner and the furnace shuts down.
How to confirm Look at the outside vents and the condensate drain, and note any odor of gas.
- 3
A poor ground or a burner problem causes a false no-flame reading
What separates it The flame looks normal but the furnace still shuts down.
How to confirm This needs a technician with a meter and the manual.
- 4
The sensor has failed or is worn
What separates it The sensor is pitted or cracked and cleaning does not help.
How to confirm Only a technician should test and replace it.
Before you touch a setting
Record this first — changing settings destroys the evidence
- The exact blink code or fault and how many seconds the flame stays.
- Whether the burners light every time and the furnace's age.
- The date of the last furnace service or inspection.
Try in this order
0 of 2 completedTest before you replace
ReversibleRecord the sequence and exact code before assuming contamination.
Weigh the repair
ReversibleReplacement difficulty for the furnace flame sensor is professional unless the exact manual permits customer maintenance.
Stop boundary
When this stops being a self-service repair
- !Do not open the burner compartment or bypass the sensor; the flame sensor is a gas-safety component.
- !Leave the house and call the gas utility if you smell gas.
Evidence ledger
Sources behind this answer
Exact questions
Common questions
Why does my furnace light and then shut off?+
A common cause is a flame sensor that cannot confirm the flame, but a technician should confirm it. Clean-sensor advice online involves opening a gas appliance, which you should not do yourself.
What does the flame sensor do?+
It confirms the burner has lit. If it cannot sense flame, the furnace shuts the gas off after a few seconds.
Why does it need cleaning?+
A thin coating can build up on the rod and stop it sensing. A light cleaning sometimes fixes shut-downs.
Who should do it?+
Turn off power and gas first. If you are not comfortable, a technician can do it quickly during a service visit.