Which device is responsible for causing a safety shutdown that requires a manual reset?

The device responsible for causing a safety shutdown that requires a manual reset is the auxiliary low water cut-off with a manual reset. This device is crucial in preventing boiler damage due to low water conditions. When the water level in the boiler falls below a predetermined safe level, the auxiliary low water cut-off activates a shutdown mechanism to stop the boiler operation. This is a critical safety feature, as operating a boiler with insufficient water can lead to overheating and potential explosions.

The requirement for a manual reset ensures that an operator must investigate the cause of the low water situation before reinitiating boiler operation. This extra step enhances safety, ensuring that an unsafe condition is not accidentally ignored. In contrast, other devices such as the automatic water level controller or the standard low water cut-off may allow the boiler to restart automatically once conditions return to normal without requiring human intervention.