The low water fuel cutoff is a device fitted to the boiler to shut the:

The low water fuel cutoff is a crucial safety device designed to protect a boiler from a potentially dangerous condition where the water level falls below a safe operational threshold. When the water level in the boiler becomes too low, this device will automatically shut the fuel valve. This action prevents the combustion process from continuing without adequate water in the boiler, which could lead to overheating and damage to the boiler or even a catastrophic failure.

By shutting off the fuel supply in response to low water levels, the low water fuel cutoff ensures that the boiler does not operate under unsafe conditions. This critical function is necessary to maintain safe and efficient operations, reinforcing the importance of the low water fuel cutoff in boiler safety systems.

The other options do not accurately describe the functionality of the low water fuel cutoff. The device does not actuate in response to high water levels or issues relating to the feed water supply. Therefore, the emphasis is on preventing low water levels from leading to unsafe conditions by cutting off the fuel supply rather than managing high water levels or the feed water supply directly.