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HomeRepair HelpFurnace RepairFurnace is frequently cycling/short cycling Repair
Furnace is frequently cycling/short cycling
01 - Dirty 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 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.
Highly Likely
02 - Furnace 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 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.
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Highly Likely
03 - Furnace Air Filter
Check and replace the furnace air filter at least twice a year, more often in dusty/dirty environments or if there is a pet in the home. A clogged air filter will greatly reduce the air flow of the furnace which can result in the unit short cycling when trying to heat the home.
Highly Likely
04 - Furnace Draft 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, or close it intermittently, 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.
Common
05 - Clogged or Restricted Vent Pipe or Heat Exchanger
The furnace has safety devices in place to prevent overheating and carbon monoxide exposure. If the exhaust flue, intake vent pipe or heat exchanger becomes clogged or restricted the burner may not stay on consistently, shutting off and then restarting several times. Check the exhaust, intake vent pipes and heat exchanger for clogs or restrictions.
Common
06 - Furnace 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. 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.
Less Common
07 - Furnace Heat Exchanger
A cracked heat exchanger can allow the hotter gas burner fumes to mix with the circulating room air. This can cause the furnace to cycle off faster but, more importantly, is a health hazard due to carbon monoxide from the burner fumes entering the home.
Less Common