Gas Furnace Limit Switch Function

A high limit control switch will turn off the gas to a furnace if the temperature becomes too high.

Gas furnace limit switch function.

When the thermostat calls for heat the furnace burners ignite and begin heating the heat exchanger. A limit switch also acts as a safety device for your furnace. The limit switch plays an important role in every normal cycle of the furnace. The limit switch includes a sensor in the heat exchanger to determine when the air is warm enough to circulate.

A limit switch is a device that s located under your furnace s supply plenum. 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. However for your own safety don t attempt to reset the switch without first consulting your furnace s instruction manual. The fan limit switch also has two other functions.

For example if the blower motor stopped running then no air would move through the unit. The flames would raise the temperature inside the unit and have no place to go getting hotter and hotter. How it works when your furnace reaches a temperature of more than 350 degrees the roll out switch shuts off. Pressure regulation automatic gas control and pilot safety.

If the plenum gets too hot the limit switch shuts off the burner. Function of the limit switch. It reads the temperature of the plenum and waits until it gets appropriately warm. 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.

When the switch turns off power is cut off to the furnace and the furnace immediately shuts down. Once the air reaches a preset temperature the limit switch turns on the blower. Details about setting the temperature controls on a fan limit switch are. Essentially this means that it determines when the hot air should be blown through your ventilation system.

Combination gas valves used standing pilot furnaces combine. It s possible to reset the switch at home when necessary by following a few simple steps. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. What is the purpose of the limit switch.

The function of your furnace limit switch is to tell the fan when to turn off and on depending on the temperature in the home. Just as it determines when the blower assembly should turn on it will also determine when it should turn off. A fan limit switch is a component of a furnace system that determines when the furnace blower assembly for hot air turns on and off. The switch is wired to the circuits of your furnace s internal power source.

The limit switch is a safety control switch located on the furnace just below the plenum.