A furnace in excellent working condition cycles automatically between on and off functions. It turns on when the sensor detects a drop in the room temperature and goes off when you achieve desired temperature levels. The process is similar to an assistant who comes as needed and doesn't overstay; hence you are less likely to think about your unit until you experience sudden failure. When your furnace starts breaking down, it will turn on and off irregularly during the day, causing what is commonly known as short cycling. Failure to investigate the cause and fix it in good time can lead to permanent system damage. If you are experiencing this issue with your furnace, consider these possible causes. 

When the Heat Exchanger Overheats

The first reason why your system might fail is the heat exchanger getting hotter than it should. Often, the overheating comes from a lack of proper airflow into the furnace. In addition, the high limit switch will likely trip to protect the unit from damage when the heat exchanger overheats. Therefore, you should check the state of the heat exchanger when your furnace keeps shutting off. 

When the Air Flow is Low

Blocked air vents are another common cause of a misfiring furnace. Different blowers need varying air volumes to function, and once you close off the air vents, you reduce the effectiveness of the blower. Consequently, the entire furnace will start switching on and off erratically because the blower is malfunctioning. You should hire a competent technician to assess your blower and determine whether it could be the reason your unit is not working. The airflow can also drop when you have dirty air filters since the blower will have a challenge pulling enough air into the heat exchanger. A dirty blower wheel also causes system malfunction because it will stop spinning as fast as it should. 

When the Flame Sensor is Corroded or Covered With Soot

Your furnace will likely keep shutting off when your flame sensor is dirty with soot or is corroded. The work of an efficient flame sensor is to detect flames and turn off the gas valve when there are no flames. But when the sensor has malfunctioned, it won't detect flames, and so it will just shut the gas valve even if there is a flame. This means no gas and, therefore, no heat. Call in an HVAC technician to fix it for you.

As long as you maintain your furnace as required, you are less likely to encounter unregulated on and off cycles. Contact a furnace repair service for more information.