What is the function of the limit switch in a gas furnace?

The limit switch in a gas furnace plays a crucial role in safety and system functionality. Its primary function is to prevent overheating by shutting off the furnace if the temperature exceeds a preset limit. This is essential because excessive heat can lead to potential hazards, including structural damage to the furnace, increased risk of fire, and reduced lifespan of the heating components.

When the furnace operates, the limit switch monitors the temperature of the airflow through the heat exchanger. If the air temperature rises too high, which may happen if airflow is restricted due to a blocked filter or a malfunctioning blower, the limit switch will open the electrical circuit, signaling the furnace to shut down. This automatic safety feature helps to protect both the furnace and the home, ensuring operation within safe temperature ranges. Therefore, the ability of the limit switch to shut off the gas supply when necessary is vital for operational safety and efficiency.