What system is used to raise the water level in an idle boiler?

The main feed system is responsible for raising the water level in an idle boiler by supplying water directly from the feed water source into the boiler. This system is crucial for maintaining the necessary water level for safe and efficient operation, especially after the boiler has been out of service and needs to be brought back online.

In practice, the main feed system typically consists of feed pumps, valves, and piping that work together to ensure a consistent and controlled flow of water into the boiler. This process is vital, as insufficient water levels can lead to dry firing and damage the boiler components.

The other systems mentioned serve different purposes. The emergency drain system, for instance, is designed for draining water from the boiler in cases of emergency rather than raising the water level. The backup reserve system typically provides additional support or redundancy for operations but isn’t the primary means of filling an idle boiler. The circulating system helps maintain flow and temperature by moving water within the boiler but does not directly address the need to fill the boiler after it has been idle. Thus, the main feed system is the correct answer.