High Limit Switch 101: Common Furnace Fundamentals

Your home's furnace relies on a delicate balance of various components working together. When those parts are all doing what they should be, the furnace engages and disengages as necessary to maintain your home's temperature. However, certain components can disrupt this operation. Here's a look at what you need to know about your heating system, the high limit switch, and the issues that it can cause.

What Is The High Limit Switch In A Furnace?

The high limit switch is a safety feature in your home's furnace. It's designed to control the system's blower fan and keep the furnace from overheating. 

Your furnace will engage when the temperature on your home's thermostat drops below the programmed level. Then, when the temperature within the burner system of the furnace reaches the limit switch level, the blower motor will engage and draw heat from within the compartment, distributing that heat throughout your home.

Once the temperature inside the house has increased enough that the thermostat shuts the furnace off, the blower fan will cycle until the temperature drops below the limit switch temperature. Then, the blower fan will shut off until the furnace engages again.

What If The Limit Switch Malfunctions?

You might wonder about how you'd know if your furnace limit switch malfunctions. There are a few key indicators that would alert you to a limit switch that isn't functioning the way that it should.

For example, if your limit switch is stuck open, you might notice that the blower fan on your furnace runs constantly. The limit switch never closes, so the fan just doesn't turn off. Alternatively, if the limit switch is stuck closed, it won't open and engage the blower fan when the furnace reaches the programmed temperature. This can cause your furnace to overheat, and it may crack the burner compartment.

How Do You Address A Faulty Limit Switch?

If you have any reason to believe that the limit switch on your furnace isn't functioning the way that it's supposed to, it's important to call a heating service technician. They can test the limit switch and safely replace it if it isn't responding properly. 

The more you understand about your furnace, its components, and how it operates, the easier it is to identify problems. The information here can help you identify potential limit switch failures and address those failures as quickly as possible. Talk with a heating services technician today for more help.