Float types use a float in a chamber piped to the boiler, and probe types sense water by electrical conductivity at a set height. Steam boilers usually have a primary cutoff, often combined with the feed pump control, and a manual-reset secondary set lower. Float types are blown down regularly, often weekly on steam, both to clear sludge from the chamber and to prove the burner actually shuts off.
Blow down the low-water cutoff every Monday, and watch the burner drop out, don't just open the valve and walk away.
A large share of heating boiler accidents trace back to low water, behind a cutoff that was jumped out, plugged with sludge or never tested.
Also heard as
- LWCO
- low-water fuel cutoff
- LWFCO
- low water
Related terms
Dry fire
To run the burner on a boiler that has lost its water, overheating and often destroying the heating surfaces.
Water column
A vertical chamber piped to a steam boiler's steam and water spaces that carries the gauge glass and level controls.
Gauge glass
The glass tube or window on a steam boiler that shows the operator the actual water level.
Lockout
A safety shutdown that holds the burner off until someone presses a manual reset.