What Causes Your Furnace to Turn On And Off Repeatedly?

You are not the only one if you are wondering why your furnace keeps shutting off. This is known as short cycling and if not corrected immediately could lead to major furnace repairs and higher utility bills. You may even be looking at a furnace replacement if you don’t diagnose the problem quickly.

1. Low Airflow

Your furnace could be shutting off because of low airflow. This could be because the air filters are dirty. Over time air filters tend to become clogged with dust and debris. Most experts recommending changing the filters every 60 - 90 days. The blower wheel on the furnace could be dirty as well causing it to go on and off quickly.

This component is responsible for pushing air. It cannot do its job properly if it is dirty. Check your air vents if your furnace keeps turning off. They may be blocked or closed. Vents should be kept open even in the rooms that are not in use.

2. Thermostat is Faulty

The thermostat controls the entire heating system. It is possible the system is turning on and off quickly because the thermostat is broken or malfunctioning. The wiring could be old and may require replacing. The thermostat batteries may need replacing. The problem could also be in the location of the thermostat.

The thermostat may turn on and off irregularly if it is placed close to direct sunlight or any other heat source. You should get a professional to take a look at it unless just the batteries needed replacement.

3. Dirty Flame Sensor

Corroded or dirty flame sensor can cause the furnace to shut off often. The sensor tells the system there is a flame and the gas valve is open. Without a flame, the sensor would shut off the gas valve as a safety measure. Dirty flame sensors don’t register the flame and turn off the gas valve. This may cause the entire system to shut down.

4. Blower Motor Turned Off

Air is circulated around the house through the blower motor. Your furnace may not run if the blower motor is turned off. The heat exchangers won’t have any air passing over them. Hold your hand to any vent in the house to determine whether air is coming out. The problem is the blower motor if the airflow is weak or is not there at all.

5. Clogged Flue Pipe

Flue pipe or the exhaust vent is located on top of the roof. It may short cycle the furnace if it is clogged with leaves, dirt, debris and sticks. Blockage can cause the furnace to overheat with a build-up of hot gases. Every furnace comes with an in-built safety mechanism that shuts it down in the event of overheating.

6. Incorrect Size of the Furnace

Furnaces that are incorrectly sized may short cycle. You have no other option but to replace the furnace in this instance. Furnaces that are too big for a house will heat it too quickly and shut down abruptly. The cycle gets repeated as the temperature begins to come down. Repeated turning on and off will also cause your utility bills to increase and you don’t want that in Northern California when energy and food costs are increasing because of new policies.