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Why Does My Furnace Turn On and Off?

By Your Advisor 3/1/16 9:35 AM Time to read:

It is completely normal for your furnace to turn on and off; that is how your furnace regulates your home's temperature. In fact, an average furnace cycles on and off anywhere between three to six times per hour. The real problem starts when your furnace turns on and off very quickly. When your system is constantly starting and stopping, it is a symptom of a system issue. But before you panic and replace your entire system, here are a few common reasons why your furnace may be short cycling.

Dirty Filter

More often than not, the reason for your furnace's short cycling is a dirty air filter. The debris from the dirty air filter obstructs the warm air flow therefore back pressure builds up causing the furnace equipment to over heat which in turn trips the high temperature limit switch. Your furnace gets the message and shuts off. Shortly after, your thermostat detects that your home is cold and starts your furnace back up again. These mixed signals drastically reduce your system's efficiency, driving up your energy bills. A simple solution is to check your filter monthly.

Malfunctioning Thermostat

Another common cause of short cycling is a faulty thermostat. Make sure you turn your thermostat on and that the set points are the ones you want. Thermostat placement can also send the wrong signals to your furnace. For example, placing your thermostat too close to a heat source (such as direct sunlight, skylights) or even drafts, windows, and doorways can affect your thermostat's readings.

Corroded Flame Sensor

A flame sensor is one of many safety features inside a gas furnace that can become damaged. Since burning fuels produce small amounts of water, the water can come in contact with the metal components inside your furnace, leading to rust. When rust accumulates, it prevents the flame sensor from functioning properly.

Ineffective Size

Choosing the correct furnace size is crucial for system efficiency. When a furnace is too large for your home, it heats your house too quickly and powers off. In turn, your home begins to cool quickly making your furnace power back on and the short cycling continues.

Consider an Upgrade

If none of the reasons above apply to your short cycling furnace, you may need to call a technician to assess whether you need a replacement. In fact, if you purchase a qualifying product and install before the end of 2016, you could be eligible to receive a federal tax credit. Call our comfort advisors at (909) 792-2222 if you'd like to set up a service appointment or schedule a service online.