What is a Furnace Limit Switch? How it Operates & Troubleshooting

What is a Furnace Limit Switch?

The furnace fan limit switch is designed to activate and deactivate the furnace blower assembly. This component is responsible for transmitting warm air throughout the air ducts in your home. In addition, the furnace limit switch is also engineered to shut down the furnace to ensure it doesn’t overheat.

What a Furnace Fan Limit Switch Looks Like

Are you having issues with the furnace fan limit switch in your heating system? Do you need to access and fix the limit switch in your unit? In order to fix issues with the switch, you will need to be able to identify this component in your system. A furnace fan limit switch features a control that is engineered to monitor the temperature within the furnace. Once the heating system reaches a specified temperature, the control will activate or deactivate the furnace to ensure optimal heating in your home.

Furnace fan limit switches also include a maximum temperature function that will disable the standard heating process if the furnace overheats. Lastly, the furnace fan limit switch may also be accompanied by a Manual On switch that allows you to keep the fan activated continuously throughout the day in your home to improve air flow.

What is a Furnace Limit Switch?How a Furnace Produces Warm Air

A furnace utilizes burners to produce heat to be distributed throughout your home. The burners are designed to heat the air produced by the air plenum in your furnace. Each burner works in conjunction with the furnace limit switch to ensure the air from the plenum is at least 20 degrees above the room temperature. Once the air is at a preset temperature, it is distributed through the heat exchanger and is transmitted to the rooms in your house. The furnace will remain activated until the temperature throughout the rooms in your home match the programmed thermostat setting.

Once your home has reached a comfortable temperature, the furnace will turn off. However, the blower assembly will remain in session until the furnace limit switch confirms the internal furnace temperature is at a safe level.

Why Do You Need a Furnace Fan Limit Switch?

The furnace limit switch is an essential component because it prevents your furnace from becoming too warm throughout standard operation. This is a safety feature that is designed to prevent damage to the internal components of your furnace and keep your family safe. In addition, the furnace fan limit switch is in charge if controlling the temperature throughout your home and eliminating cold drafts.

Adjust the Furnace Fan Limit Switch to Control the Blower

You can adjust the setting of the furnace fan limit switch to change the point at which it turns the blower on and off, although we don’t advise that you tamper with it from its factory settings. This is best left to a furnace repair specialist when trying to troubleshoot problems. The standard settings for most furnace fan limit switches are 200°F to shut off the burner, 130°F to turn off the blower, and 100°F to turn the blower back on.

What is a Furnace Limit Switch?Common Problems With Furnace Fan Limit Switches

As the furnace becomes older, it is common to experience issues with the sensor on the furnace fan limit switch. To fix the sensor, we recommend removing all dirt, grime, and other materials from the fan limit switch that may be inhibiting your furnace from operating correctly. If your furnace is continuously activating and deactivating throughout the day, this may also be a sign of a blower motor issue. An overheated blower assembly will trip the furnace limit switch and cause your furnace to deactivate prior to the end of the standard heating cycle.

Other common issues that may affect the furnace fan limit switch include faulty gas valves, thermostats, and circuits. Lastly, we always recommend checking the filter in your furnace to confirm it isn’t clogged. A clogged air filter may cause the plenum in your furnace to reach an unsafe temperature. Once the plenum overheats, the furnace limit switch will turn off the furnace to keep you safe. To receive help with a furnace limit switch repair, give our contractors a call by phone at (484) 206-8594 or schedule an appointment online to receive assistance. To prevent future issues with your furnace limit switch, we recommend performing standard furnace tune-ups and repairs. Our team of HVAC technicians offer heating services such as Furnace Repair, boiler installation, and heat pump replacement for small to large homes in West Chester, Coatesville, Darby, and other areas of Pennsylvania.

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