Unfortunately, an alarming number of boilers equipped with low-water trips are destroyed each year. There are several common reasons for low-water trip failures. Disabled trip circuits. A typical scenario involves bypassing the switches to eliminate nuisance trips due to improperly tuned controls, safety device failure, etc. This approach is a Band-Aid to cover the real problem and should never be allowed.
Inoperative trip switches.
Trip switches should be blown down regularly to exercise the trip devices and remove potential sludge buildup. A properly designed installation allows the trip devices to be blown down each shift without the boiler tripping offline. This blowdown keeps them clean and verifies proper operation of the low-water protection and alarm circuitry. Water that enters the boiler is vaporized to steam, leaving solids behind in the form of scale or buildup in the areas of highest heat transfer rate. A buildup of scale deposits inside boiler tubes produces an insulating layer which inhibits the ability of the water to remove heat from the tube surface.