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Flame 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 the voltage to the gas valve to prevent the furnace from heating. 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 furnace still doesn’t heat, replace the flame sensor.
Draft Inducer Motor
The draft inducer motor draws air into the heat exchanger and then exhausts it out of the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper airflow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the furnace to shut off after a few minutes. If the ignition process stalls, the furnace will shut off. If the draft inducer motor is at fault, replace it.
Flame Rollout Limit Switch
The flame rollout switch monitors the heat surrounding the burners. If the inducer fan motor cannot draw enough air through the burners, or if the furnace is not venting properly, the rollout switch will open to halt the ignition sequence and prevent the furnace from heating. When this happens, the furnace will shut off after running for a few minutes. To determine if the flame rollout switch is defective, use a multimeter to test it for continuity. If the switch does not have continuity, replace it. Be aware that poor airflow through the burner is often a result of insufficient ventilation or a restricted exhaust vent. Make sure that your furnace is in a properly ventilated location and that the exhaust vent is clear of obstructions.
Pressure 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 ignition process to stall. 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.
Air Flow Problem
The furnace must have proper airflow through the burner 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 obstructions at the air inlet.
Control 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, causing the furnace to shut off after a few minutes.