Boiler Fault — Low Water Cutoff

What This Fault Means

A low water cutoff (LWCO) fault shuts down the burner when the boiler water level drops below the safe minimum. Operating a boiler with low water risks catastrophic overheating and pressure vessel failure.

Common Causes

• Feedwater pump failure or low feedwater supply
• Steam leak or blowdown valve left open
• LWCO probe fouled with scale or sediment
• LWCO float stuck in the up position (mechanical type)
• Feedwater control valve malfunction

Recommended Fix

1. DO NOT attempt to add cold water to an overheated boiler — this can cause thermal shock.
2. Verify the sight glass water level visually.
3. Check the feedwater pump operation and supply tank level.
4. Inspect and clean the LWCO probe or float per manufacturer schedule.
5. Test the LWCO by slowly draining water until it trips — it should shut the burner before the sight glass goes empty.