When a furnace is in good working condition, it will turn on and continue running until your home reaches your desired temperature. Short cycling means that the furnace will turn on for a short amount of time, turn off, then start up again a couple of minutes later. If you notice that your furnace is short cycling, don't brush it off or ignore it — short cycling almost always indicates that there is something wrong with the furnace, and repairs are needed to solve the issue. Some of the most common reasons why a furnace short cycles includes:
Limit Switch Needs to Be Replaced
A furnace is equipped with a limit switch that monitors the temperature of the heat exchanger. A functional limit switch will send a signal to the furnace to shut off if the heat exchanger gets too hot. Over time a limit switch can fail, and when it does, your furnace may begin short cycling. A bad limit switch will not be able to correctly sense the temperature, so it will tell the furnace to turn off even if the heat exchanger is not too hot. After the furnace turns off, it will start up again and the cycle will continue. An HVAC technician can replace the bad limit switch to resolve the problem.
Bad Flame Sensor
The flame sensor inside a furnace is designed as a safety feature to ensure that there is a flame present while gas is flowing into the furnace. If there is not a flame, the furnace will not turn on, as it is dangerous for gas to flow through the furnace without a flame being present. When the flame sensor goes bad, the furnace will get the wrong signals and it will continually turn off and on. In this type of situation, it may be difficult to heat up your home since the furnace won't run for long before turning off. Contact an HVAC professional to have your flame sensor inspected and replaced.
Failing Blower Motor
A blower motor continually pushes air through the furnace, which helps make sure that it does not overheat. When the blower motor fails, too much hot air will build up inside the furnace and the limit switch will tell the furnace to turn off in order to avoid overheating. If your furnace is short cycling due to a failing blower motor, you will most likely notice that the furnace makes strange sounds when it turns on.
Contact a local furnace repair service to learn more.