What does a high-limit control do in a boiler?

The high-limit control in a boiler serves a critical safety function by shutting down the boiler if the water temperature exceeds a predetermined limit. This mechanism is vital for preventing dangerous conditions, such as overheating, which can lead to equipment failure or catastrophic incidents. By monitoring the temperature, the high-limit control ensures that the boiler operates within safe parameters, protecting both the equipment and personnel.

In contrast, the other options describe functions that are not the purpose of the high-limit control. While increasing boiler pressure can be a part of operational adjustments, it is not related to safety shutdowns imposed by temperature. Maintaining a constant water level is managed by different controls specifically designed for water level management, such as feedwater controls or level sensors. Enhancing fuel combustion efficiency involves burner technologies and control strategies but is unrelated to the high-limit control's role in monitoring temperature.