What is the purpose of a low water cut-off in a boiler?

A low water cut-off is a critical safety feature in a boiler system designed to monitor the water level within the boiler. Its primary purpose is to shut down the boiler when the water level drops below a predetermined safe point. If the water level becomes too low, the boiler may overheat, which could lead to damage or even catastrophic failure. By automatically shutting down the boiler, the low water cut-off helps to protect the integrity of the system and ensure safe operation.

In contrast, other options do not accurately describe the function of a low water cut-off. For instance, mechanisms that prevent overfilling or regulate fuel flow serve different purposes related to the feedwater system or combustion processes, respectively. Additionally, controlling air supply is a separate aspect of boiler operation focused on enhancing combustion efficiency and safety, but it does not pertain to monitoring water levels. Thus, the correct answer highlights the essential role of the low water cut-off in maintaining safe boiler operation.