In the context of furnace operation, what does a high limit switch do?

The high limit switch plays a crucial role in furnace safety and operation by preventing the furnace from overheating. When the temperature in the furnace reaches a specific upper limit, the high limit switch automatically interrupts the power supply to the burners, stopping the heating process. This function is essential to protect the furnace and the entire heating system from potential damage that can occur due to excessive heat, which could lead to equipment failure or even pose a fire hazard.

In contrast, while one might think of the high limit switch in relation to room temperature control, that is not its primary function; instead, it is specifically concerned with the furnace's operational safety. Regulating gas flow to the burners and measuring fuel efficiency are also not roles performed by the high limit switch; those are managed by different components of the heating system.