Furnace limit switches are typically wired in series with what component?

Furnace limit switches are typically wired in series with the gas valve to ensure safe operation of the furnace. The primary function of a limit switch is to monitor the temperature within the heat exchanger. If the temperature exceeds a predetermined limit, the switch opens the circuit, cutting off power to the gas valve. This prevents the furnace from continuing to heat and potentially causing overheating or unsafe conditions.

When the limit switch is wired in series with the gas valve, it ensures that if an unsafe temperature condition arises, the gas supply is interrupted immediately, halting combustion and allowing the furnace to cool down. This is a critical safety feature that helps protect the system and the occupants of the space it heats.

In contrast, components like the blower motor, thermostat, and flame sensor have different roles within the heating system. The blower motor is controlled by the thermostat and operates to circulate air throughout the space, while the thermostat measures room temperature to regulate the heating system's operation. The flame sensor detects the presence of a flame to confirm that combustion is taking place, but it does not directly interface with the gas flow in the same safety-critical way as the limit switch does with the gas valve.