Which safety feature prevents a boiler from operating under low-water conditions?

The low-water cut-off device is a critical safety feature designed specifically to protect a boiler from operating under low-water conditions. When the water level in the boiler drops to a predetermined level, the low-water cut-off device senses this condition and automatically shuts down the boiler's operation. This is essential because operating a boiler without sufficient water can lead to overheating, damaging the boiler's components, and creating a dangerous situation.

Other safety devices, such as pressure relief valves, expansion tanks, and safety valves, serve distinct purposes. A pressure relief valve is meant to release excess pressure to prevent over-pressurization of the boiler, while an expansion tank accommodates thermal expansion of water in the system, and a safety valve is designed to provide safety against pressure buildup. None of these devices directly address the issue of low water levels, which makes the low-water cut-off device indispensable in boiler safety.