Which of the following is a safety device used in heating systems to prevent overheating?

The high-limit switch is a crucial safety device used in heating systems to prevent overheating. It functions by monitoring the temperature within the system. When it detects that the temperature exceeds a preset limit, the high-limit switch automatically shuts off the heating source to prevent potential damage to the system or even hazards like fire. This proactive measure ensures that the heating equipment remains within safe operating temperatures, enhancing the overall safety and reliability of the heating system.

In contrast, while devices like pressure relief valves and flow switches also play important roles in the operation of heating systems, they do not specifically address the issue of overheating in the same direct manner. The pressure relief valve is designed to relieve excess pressure, which is more relevant to preventing pressure-related hazards than controlling temperature. Similarly, a flow switch is used to monitor water or air flow, ensuring that circulation occurs properly but does not inherently manage temperature levels. A temperature gauge, while useful for displaying temperature readings, does not take any action to prevent overheating; it merely provides information about current operating conditions.