How should a limit safety check be conducted on a gas furnace?

Conducting a limit safety check on a gas furnace involves ensuring that the safety mechanisms, specifically the limit switch, are functioning correctly. This check is vital as it confirms that the furnace will turn off if it overheats, ensuring safety and preventing potential hazards.

Stopping the blower operation for at least 10 minutes allows the technician to observe how the furnace reacts under high-temperature conditions without the cooling effect of the blower. This is important because if the limit switch is functioning properly, the furnace should shut down once it reaches the set limit temperature, indicating it is effectively protecting against overheating.

In contrast, other options do not adequately assess the limit safety function. Continuous blower operation would not allow the furnace to reach the limit temperature, and increasing the thermostat setting to maximum could lead to unsafe operation without testing the pivotal aspect of the limit switch’s performance. Measuring gas pressure at the burner is more related to fuel delivery and combustion efficiency, rather than directly testing the limit safety functions. Hence, stopping the blower allows for a direct assessment of the limit switch's operation in a controlled manner.