Furnace Heat Limit Switch

A furnace has two switches called a fan limit switch and a high limit switch these switches can be separate or in one package called a combination switch.

Furnace heat limit switch.

The furnace oil or gas burner should turn on and subsequently the fan limit control should turn the burner back off when the temperature in the supply air plenum reaches the fan limit set point. This happens because the flames are not being drawn into and throu. The limit switch plays an important role in every normal cycle of the furnace. This control also provides a safety limit that turns off the burner or furnace if temperatures at the furnace are too high.

Watch the dial on the fan limit switch moving to confirm its operation. One common symptom of a failing or blocked heat exchanger is the roll out switch tripping. Fan limit switches are used on all types of building heating furnaces. Once the plenum reaches a specific temperature the limit switch sends a signal to the air handler to begin running and delivering warm air to your home.

A limit switch is a device that s located under your furnace s supply plenum. Watch the oil or gas burner. Initially the air above the heat exchanger in the supply plenum is not warm enough to blow into the house so the limit switch keeps the blower off. The fan limit switch on a heating furnace controls when the furnace blower fan turns on and off.