Which safety control prevents water in a boiler system from becoming super-heated?

The pressure-relief valve is a critical component in boiler systems that serves the specific purpose of preventing water from becoming super-heated. In a closed boiler system, pressure can build up due to high temperatures and the expansion of water. If the pressure exceeds safe limits, there is a risk of water becoming super-heated, which can lead to explosive conditions.

The pressure-relief valve is designed to automatically open when the pressure reaches a predetermined level, allowing excess steam or water to escape and thereby reducing the pressure within the system. This action helps maintain the safe operation of the boiler by ensuring that conditions remain within safe parameters, effectively preventing the risk of super-heating, which can cause serious safety hazards.

In contrast, the other components, while important for the operation of a boiler system, serve different functions. The backflow preventer is utilized to prevent contaminated water from entering the potable water supply, the circulator is responsible for moving water through the heating system, and the pressure-reducing valve regulates the pressure in system supply lines. Each of these parts contributes to system operation and safety but does not directly prevent water from becoming super-heated as the pressure-relief valve does.