Furnace Short-Cycling? Causes And Troubleshooting | Square One

The important points

• Furnace short-cycling refers to a furnace that’s switching on and off too frequently.
• Short-cycling can result in undue wear and tear on the furnace.
• There are several issues that can cause a furnace to short-cycle, most of which are easy to fix.

What is furnace short-cycling?

Furnace short-cycling refers to a furnace that’s switching itself on and off too frequently.

It’s normal for a furnace to turn on and off periodically. They are designed to cycle on and off, but a standard home furnace should only turn on and off between three to eight times per hour. That means normal heating cycles last from seven to 20 minutes.

You can tell your furnace is short-cycling if that on/off cycle happens every couple of minutes. If that’s the case, there’s probably something wrong.

While it’s undoubtedly an issue, short-cycling does have a silver lining: it demonstrates that the furnace’s safety mechanisms are working and preventing something a serious problem—a fire starting and burning down your home, for example.

Before you investigate the cause of a short-cycling furnace, it’s helpful to understand how your furnace works. Basically, the blower motor—the fan that distributes the air—sends air across a heat exchanger comprised of tubes with burning fuel passing through them, and then onward into the rooms of your home.

Luckily, there are numerous safety features in place that prevent the furnace from doing so in an unsafe manner. A high limit switch turns the furnace off if it becomes too hot, while a flue limit switch shuts off the furnace if it isn’t venting properly through the exhaust flue.

Short-cycling can affect both gas and electric furnaces, for many of the same reasons.