Gas Furnace Limit Switch Function

When the switch turns off power is cut off to the furnace and the furnace immediately shuts down.

Gas furnace limit switch function. The fan limit switch also has two other functions. It prevents overheating by interrupting the circuit to the gas valve. A limit switch also acts as a safety device for your furnace. It reads the temperature of the plenum and waits until it gets appropriately warm.

If the temperature inside of the plenum gets too hot it shuts off the gas supply to your burners to prevent your. The switch is wired to the circuits of your furnace s internal power source. A limit switch is a device that s located under your furnace s supply plenum. Combination gas valves used standing pilot furnaces combine.

When the thermostat calls for heat the furnace burners ignite and begin heating the heat exchanger. How it works when your furnace reaches a temperature of more than 350 degrees the roll out switch shuts off. Just as it determines when the blower assembly should turn on it will also determine when it should turn off. 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.

What is the purpose of the limit switch. 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. However for your own safety don t attempt to reset the switch without first consulting your furnace s instruction manual. For example if the blower motor stopped running then no air would move through the unit.

The limit switch is a safety control switch located on the furnace just below the 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. If the plenum gets too hot the limit switch shuts off the burner. Pressure regulation automatic gas control and pilot safety.

A high limit control switch will turn off the gas to a furnace if the temperature becomes too high. Details about setting the temperature controls on a fan limit switch are. The limit switch plays an important role in every normal cycle of the furnace. Essentially this means that it determines when the hot air should be blown through your ventilation system.

Function of the limit switch. The limit switch includes a sensor in the heat exchanger to determine when the air is warm enough to circulate. The flames would raise the temperature inside the unit and have no place to go getting hotter and hotter. By keeping the fan off until the supply air plenum is warm the heating furnace limit switch prevents the furnace blower from sending chilly air into the building if the oil or gas burner has not sufficiently heated up the furnace heat exchanger and supply air plenum.

It s possible to reset the switch at home when necessary by following a few simple steps.