Maryland HVAC Masters Practice Test

A low-water cut-off is a safety device that protects a boiler by stopping heat when the water level is too low. Water is needed to absorb heat and protect the boiler tubes from overheating. If the water level drops, the remaining water can’t efficiently absorb heat, and exposed surfaces can overheat, warp, or fail. The low-water cut-off monitors the water level with a float or electronic sensor and, when the level falls to a dangerous point, it interrupts the burner or fuel supply (or its control circuit) to shut the boiler down until water is restored. That’s why the correct function is to shut off the boiler if the water level is too low. It isn’t used to regulate temperature, drain condensate, or increase pressure.