Boiler Pressure Keeps Dropping: Causes & Fixes

Understanding Boiler Pressure

Industrial boiler pressure is maintained by the balance between steam generation (from the burner) and steam consumption (by process equipment). When pressure drops continuously, the system is consuming steam faster than the boiler can produce it, or steam is being lost through leaks, blowdown, or failed traps.

Common Causes (Ranked by Frequency)

• 1. Failed-open steam traps: The #1 cause. Live steam blowing through failed-open traps into the condensate return wastes steam continuously. Survey all traps — see our Steam Trap Testing guide.
• 2. Steam leaks: Leaks at flanges, valve packings, or damaged piping waste steam directly. Even a 3mm hole on a 10 bar system wastes 25 kg/hr.
• 3. Process demand exceeds boiler capacity: If the plant has expanded or new equipment has been added, the boiler may be undersized. Check: compare actual steam demand against rated capacity.
• 4. Blowdown valve passing: If the bottom or surface blowdown valve isn't fully closed (worn seat, debris), water and steam are continuously lost. Check: feel the blowdown discharge pipe — it should be cold when blowdown is closed.
• 5. Safety relief valve weeping: A relief valve that doesn't seal properly allows steam to escape continuously. Check: look for steam at the relief valve discharge pipe.
• 6. Fouled boiler tubes: Scale or soot on tubes reduces heat transfer — the burner fires at full capacity but can't generate enough steam. Check: rising stack temperature is the key indicator.
• 7. Burner underfiring: The burner may not be reaching full firing rate — check fuel pressure, modulating motor stroke, and combustion air supply.
• 8. Feedwater too cold: If the deaerator or economiser isn't performing, cold feedwater requires more energy to heat, reducing steam output. Check: feedwater temperature should be above 90°C.

Diagnostic Flow

1. Is the burner at high fire? If yes, the boiler is trying but can't keep up. If no, investigate the burner control system.
2. Is the stack temperature high? If yes, tubes are fouled — clean them. If normal, heat transfer is adequate.
3. Survey all steam traps. Failed-open traps are the most common cause of continuous pressure drop.
4. Walk the distribution system. Look for visible steam leaks at flanges, valves, and piping.
5. Check the blowdown valve. Feel the discharge pipe — it should be cold when the valve is closed.
6. Check the relief valve. Look for steam at the discharge — a weeping valve needs recertification or replacement.
7. Compare demand vs capacity. If all else checks out, the boiler may be undersized for the current load.