What is the function of an auxiliary limit control?

The correct answer highlights the primary role of an auxiliary limit control, which is to activate a shutdown in the system when overheating is detected. These controls are essential for safety in gas appliances, as they monitor the temperature and are designed to cut off the operation of the appliance to prevent damage or hazards, such as fire or equipment failure.

In essence, when the temperature exceeds a predetermined threshold, the auxiliary limit control will trigger, shutting off the gas supply to the burner. This safety feature ensures that appliances operate within safe temperature ranges, and is crucial in preventing dangerous situations that could arise from overheating.

Other choices may touch on important aspects related to gas systems, such as regulating air flow or ensuring safe operations, but they do not encapsulate the specific function that the auxiliary limit control performs in the context of overheating situations. Therefore, the focus on its activation during overheating explains why this choice is the right answer.