What is the purpose of a high fire limit control on a boiler?

The purpose of a high fire limit control on a boiler is to ensure that the boiler does not operate beyond a safe level, specifically in terms of temperature and pressure. This type of control functions as a safety mechanism to prevent dangerous conditions that may arise if the boiler were to fire at excessive levels without proper ventilation.

While option B mentions ensuring adequate purge air flow, which is related to safety, the focus of high fire limit controls is on monitoring the boiler's combustion process and preventing overheating. They are designed to shut down the burner if the temperature or pressure exceeds a predetermined setpoint, thus protecting the boiler from failure or dangerous incidents.

In this context, it's important to clarify that while the other options mention relevant aspects of boiler operation—like monitoring water levels, measuring temperature fluctuations, or adjusting fuel supply—they do not specifically pertain to the primary function of high fire limit controls. The high fire limit control plays a crucial role in managing combustion safely rather than directly influencing air flow or other operation parameters.