||Fuse or Circuit Breaker
||Either the power switch has blown, or the electrical system associated with your furnace has shorted.
||Either replace the blown switch or reset the circuit breaker associated with your furnace.
||The furnace’s igniter is either cracked or defective.
||If the igniter is cracked, replace it. If it isn’t, test with a multimeter for continuity.
||The furnace’s thermostat is adjusting incorrectly.
||Use your thermostat’s adjustable calibration scale to adjust the heat anticipator. If this doesn’t work or you don’t have a scale, replace the thermostat.
|Not blowing hot air?
||Either the blower motor in your furnace has burned out, or the connecting belt has snapped.
||If the blower motor is receiving power but isn’t running, the motor has failed. If it does run, then the connecting belt has broken. Replace either the motor or belt depending on the outcome.
|Blowing too much air?
||The relay responsible for regulating the amount of voltage that your blower motor receives has failed, resulting in the continual sending of voltage to the motor.
||Replace the control board.
||The contact that controls the blower motor on your thermostat could be stuck closed.
||Use a multimeter to check for continuity. If it appears that the thermostat is the issue, replace it.
|Starting and then stopping shortly after?
||If the flame sensor is either defective or dirty, it will not be able to detect whether or not a flame is present.
||If dirty, use a fine abrasive pad to clean the sensor. If faulty, replace the flame sensor.