Gas Fitter Practice Test

If the high limit switch activates due to overheating, what is the immediate effect?

1. Gas valve remains open

2. Blower speed increases

3. Circulating pump operation halts

4. Furnace operation stops

The correct answer is: Furnace operation stops

When the high limit switch activates due to overheating, the immediate effect is that it stops the furnace operation. The high limit switch is a critical safety device designed to prevent the furnace from overheating. When the temperature within the furnace exceeds a predetermined safe limit, this switch opens, cutting off power to the entire heating system. This action is crucial because it protects the furnace and surrounding components from damage that could occur due to excessively high temperatures. The functioning of the high limit switch ensures that the furnace operates within safe temperature parameters, preventing potential hazards such as fires or equipment failure. When the furnace operation stops, it allows the system to cool down before it can safely resume normal function, thus maintaining the integrity and safety of the heating system. Other options, such as the gas valve remaining open or the blower speed increasing, would not typically occur when the high limit switch is activated, as those actions could further contribute to overheating and compromise safety. Similarly, a circulating pump halting does not directly relate to the function of the high limit switch in the context of furnace safety.