As a southeast Michigan homeowner, it is important to understand what a limit switch is on a furnace, how it works, and why it’s important to the safety of your home, family, and heating system. While there are a number of safety features in most furnaces, understanding the function of the limit switch is important.

What Does a Furnace Limit Switch Do?

There are two primary functions of a limit switch. One, until the air generated inside the furnace, warms up sufficiently, the limit switch will not allow the fan to come on. Two, if the temperature of the air around the heat exchanger should become too hot, the limit switch essentially “kills” the burner. Manufacturers design limit switches to shut the burner off in situations where the temperature around the heat exchanger is too high in order to prevent a potential crack of the heat exchanger, which would result in toxic byproducts of combustion escaping into your home. This is dangerous!

The Most Common Issues with Limit Switches

As with any equipment, components of your heating system can malfunction; this includes the limit switch. If your furnace’s blower continues to operate without shutting off, it may be that the limit switch is malfunctioning; this is the most common symptom of a problem. Just as it won’t allow the fan to come on until the air has warmed to a certain temperature, the limit switch will shut down once the air cools to a certain degree. If your furnace’s blower continues to run and doesn’t cycle off, it could be the result of a limit switch that is beginning to go bad.

Under certain circumstances, the limit switch will prevent your furnace from operating. This is the case when a clogged air filter prevents sufficient air from circulating through the system, which ultimately limits airflow and may cause the heat exchanger to become overly heated. The limit switch will turn the burner off when it senses an overheated heat exchanger.

Safety should be a top priority this winter season for homeowners not only in Ann Arbor, Ypsilanti, Howell, and surrounding areas but throughout Michigan. Have questions about the limit switch or other safety features of your furnace? Give Haley Mechanical a call today.

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