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Fasco Furnace Burners Won’t Stay Lit

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.

Most Frequent Causes for Furnace burners won’t stay lit

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Cause 1Gas Supply Problem

Check 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.

Cause 2Control Board

The control board regulates the power supply to all of the components of the furnace. If the control board is defective, it might not send voltage to the ignition system, preventing the burner from staying lit.

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Cause 3Clogged or Restricted Vent Pipe or Heat Exchanger

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.

Cause 4Igniter

The igniter gets very hot and glows bright orange to light the gas burner. If the igniter fails, the gas won't continue to be ignited and the burners won't stay lit. To determine if the igniter is faulty, remove the igniter and inspect it for cracks. If the igniter is cracked, replace it. If the igniter is not cracked, use a multimeter to test the igniter for continuity. If the igniter does not have continuity, replace it.

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Cause 5Improper Vacuum or Pressure

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.

Cause 6Flame Sensor

The flame sensor monitors the burner to detect whether or not a flame is present. If the flame sensor is defective, it might fail to detect a flame. If the flame sensor does not detect a flame, the control board will shut off voltage to the gas valve resulting in the burners not staying lit. Sometimes, if the flame sensor is dirty, it will fail to detect a flame. Try cleaning the flame sensor with a fine abrasive pad. If the burners still won't stay lit, replace the flame sensor.

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Cause 7Pressure Switch

The pressure switch closes when the burner has sufficient airflow. If the pressure switch isn’t working, it might not close when the proper airflow is present, causing the burners not to stay lit. If the ignition process stalls, the furnace will shut off. To determine if the pressure switch is defective, use a multimeter to test the switch for continuity. If the pressure switch does not have continuity, replace it.

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Cause 8Hose

The air traveling through the pressure switch hose will put a negative pressure or vacuum on the switch, causing it to close when the burner has sufficient airflow and allowing the ignition process to continue. If the hose has a hole in it, or is not securely fastened to the switch, the pressure switch may only close intermittently, causing the burners to not stay lit. Inspect the pressure switch hose for any damage and replace if necessary.

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Cause 9Tube

The air traveling through the pressure switch tube will put a negative pressure or vacuum on the switch, causing it to close when the burner has sufficient airflow and allowing the ignition process to continue. If the tube has a hole in it, or is not securely fastened to the switch, the pressure switch may only close intermittently, causing the burners not to stay lit. Inspect the pressure switch tube for any damage and replace if necessary.

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Cause 10Air Flow Problem

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.

Cause 11Draft Inducer Motor

The draft inducer motor draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the burners not to stay lit. If the ignition process stalls, the furnace will shut off. If the draft inducer motor is at fault, replace it.

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Cause 12Draft Inducer Motor Assembly

The draft inducer motor assembly draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor assembly is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the burners not to stay lit. If the ignition process stalls, the furnace will shut off. If the draft inducer motor assembly is at fault, replace it.

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