||Fuse or Circuit Breaker
||Your furnace’s electrical system has potentially shorted, or the power switch has blown.
||Reset the furnace-associated circuit breaker. If it has blown, you will have to replace it.
||The furnace’s igniter might either be cracked or defective.
||Check the part for cracks, replace the igniter if it’s cracked.. If it isn’t, test with a multimeter for continuity.
||Your unit’s thermostat might be adjusting incorrectly.
||Should the thermostat have an adjustable calibration scale, use this to adjust the heat anticipator. If this doesn’t work or you don’t have a scale, replace the thermostat.
|Not blowing hot air?
||The blower motor might be burnt out. If this doesn’t seem to be the case, then the connecting belt may have snapped.
||First, see if power is reaching the motor. If it is but isn’t running, the motor has failed. If the motor runs but air doesn’t move, the connecting belt has probably broken. Replace the belt.
|Blowing too much air?
||If the relay that regulates the blower motor on the control board has failed, it will continually send voltage to the motor.
||Replace the control board.
||The contact that controls the blower motor on your thermostat may be sticking.
||Use a multimeter to check for continuity. If it appears the thermostat is the issue, replace it.
|Starting and then stopping shortly after?
||Your furnace’s flame sensor detects if a flame is present. If it is either defective or dirty, it will not be able to detect a flame.
||If dirty, use a fine abrasive pad to clean the sensor. If faulty, replace the flame sensor.