The part(s) or condition(s) listed below for the symptom Furnace burners won’t stay lit are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
Furnace Blower Not Running? Gas Furnace Troubleshooting
Furnace Blower Runs All The Time? Gas Furnace Troubleshooting
Furnace Noisy Or Loud? Gas Furnace Troubleshooting
Furnace Starts Then Stops? Gas Furnace Troubleshooting
Furnace Not Heating? Gas Furnace Troubleshooting
Replace Furnace Filters - Tech Tips from Repair ClinicCheck the gas control valve to ensure that it is turned on and there is gas present at the valve. Natural gas pressure should be close to 4 inches water column at the furnace input; propane pressure close to 11 inches water column at the furnace input. The gas pressure can be checked with a manometer at the valve. Low gas pressure can cause a weak flames and inconsistant lighting.
Control Board
If the flame rollout limit switch is tripping a restricted or cracked heat exchanger, or restricted outlet pipe, could be preventing the flame from being drawn through the heat exchanger properly. This can be very dangerous and the furnace should be inspected by a qualified service technician. You should never keep resetting the rollout limit without fixing the problem. If the heat exchanger is cracked, carbon monoxide can enter the home's venting system causing death. It is recommended to have at least one carbon monoxide detector on each floor of the home.
Igniter
The draft inducer fan motor assembly creates a vacuum when running which closes the pressure switch. Check the pressure hose and port on the inducer assembly for leaks or obstructions. A clogged condensate trap or drain, or restricted heat exchanger, can also cause a pressure switch to not function. Replace the pressure switch if there is proper vacuum or pressure but the switch is not working properly. You can test the pressure switch for electrical continuity with a multimeter. The contacts will either close or open depending on the application.
Flame Sensor
Pressure Switch
Hose
Tube
The furnace has two seperate requirements for air flow. The homes air is heated and recirculated through the heat exchanger and heat ducts through an air filter. A clogged air filter can cause the furnace to overheat and shut down, and should be replaced at least twice a year depending on the type of filter and environment. The furnace must also have proper airflow through the burner and heat exchanger in order to continue running. The furnace draws air from the surrounding area or from outside the room. If the furnace is located in a utility closet or in a cramped storage room, there may not be sufficient available air for the furnace to heat properly. If the furnace draws air from outside the home, check for an obstructions at the air inlet.
Draft Inducer Motor
Draft Inducer Motor Assembly
