||The electrical system that powers your furnace has likely shorted.
||Reset the circuit breaker that’s associated with your furnace.
||The igniter might either be cracked or defective.
||Check to see if the igniter is cracked and needs replacing. Otherwise, test it with a multimeter for continuity.
||The thermostat might be adjusting incorrectly.
||If your thermostat has an adjustable calibration scale, use it to adjust the heat anticipator. If this doesn’t work, replace the thermostat.
|Not blowing hot air?
||Either the blower motor is burnt out, or the motor’s connect belt has snapped.
||See if power is reaching the motor. If it is, but the motor isn’t running, replace the motor. If the motor runs but air doesn’t move, the connecting belt has snapped. Replace the belt.
|Blowing too much air?
||Your furnace’s blower motor is continually being sent voltage due to a failed relay on the control board.
||You will have to 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 the part.
|Starting and then stopping shortly after?
||The 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.