What is the basic function of a low-water cutoff?

• A. Stops fuel and/or firing if water level drops below a safe point to prevent boiler damage
• B. Increases water level automatically
• C. Controls feedwater pump speed
• D. Measures steam pressure

Answer: (A)

At its core, the low-water cutoff is a safety device that prevents firing when the boiler water level has fallen to a point where it cannot safely absorb the heat. When the water drops below that safe point, the device automatically stops the fuel supply and/or the firing. This instantly protects the boiler from overheating, which can cause tube damage, warped metal, or more serious failure. It’s different from indicators or control systems that merely show or adjust water levels; it actively intervenes to shut things down if the level is too low. It also isn’t about increasing water level or controlling feedwater pump speed—those are separate functions. In short, its job is to shut off fuel and/or firing if water is too low to prevent boiler damage.