Boiler Operation and Water Level Management
The gauge glass rules everything
The normal water level is at the middle of the gauge glass. The water column holds the glass above the mud line so sediment does not block it. Blow the glass down every shift: open the drain with both valves open; close the upper valve to prove the bottom connection; close the lower and open the upper to prove the top connection; close the drain, reopen both, and watch the level return quickly. Slow return or a level that does not move when firing rate changes means a partially plugged connection - a false level, which is more dangerous than no reading.
Low water and carryover
If the low-water fuel cutoff trips, the burner shuts down. Do not reset it until the level is re-established and the cause found. If the glass is empty, secure the fuel, let the boiler cool, and inspect for a distorted crown sheet or tube before adding any water - dumping feedwater onto an overheated crown sheet is a classic route to a violent failure. High-or-erratic level, water in the steam line, or a level that surges when the burner lights points to foaming or priming, usually from high dissolved solids, alkalinity, oil, or a sudden load swing. Correct it with surface (continuous) blowdown, water treatment, and reduced firing - not by simply adding feed.
Bottom blowdown removes sludge and sediment; surface blowdown controls dissolved solids and foam. Blow down at low fire with the level near the top of the glass, and never leave a blowoff valve unattended.
Rule of thumb: short, frequent bottom blows beat one long, deep pull - a long pull stresses tubes and can drop the level low enough to trip the cutoff.