Get Started Free

Steam pressure drop: the failure signature

Technical review pending. This guide is based on the cited manufacturer documentation; check it against the manual for your exact model and firmware before acting.

The steam-pressure control raises the firing rate when pressure falls below setpoint. A pressure drop therefore means either the burner did not fire up, or firing up was not enough. Putting steam pressure, steam flow and firing rate on one chart separates the two in a few minutes.

Illustrative pattern · simulated, not plant data

Steam flowFiring rateSteam pressureDemand rises
Capacity variant: steam demand rises, the firing rate reaches 100% and stays there, and pressure still sags until demand falls.
Diagnose this with AI

Upload a trend export (CSV or Excel) or a screenshot of the trend around the event. InduQT lines up which signal moved first and compares it with these variants.

Try Free Boiler Diagnostic

Where it shows up

Signals to trend

SignalWhat it does in this failure
Steam pressureThe symptom. Note how fast it falls and whether it recovers.
Steam flowRising steam flow during the drop means demand rose; flat flow means the boiler is not delivering.
Firing rateAt 100% during the drop: capacity or heat transfer. Not rising: control, a low-fire hold or manual mode.
Main gas pressureLow fuel pressure at high fire caps the real firing rate even when the control asks for more.
Burner sequence stateA lockout or recycle at the start of the drop means the pressure loss is a consequence of a trip.
Stack (flue gas) temperatureRising over months at the same load points to fouled heating surfaces limiting output.

Variants: what moves first, and what it points to

1Demand above firing capacity

Points to it
Steam flow rises above its normal peak; firing rate pinned at 100%; pressure recovers when demand falls.
Check
Compare peak steam flow with the boiler rating; stagger large loads or bring another boiler online.

2Burner does not fire up

Points to it
Pressure falls but firing rate stays low or modulates down; modulation in manual or a low-fire hold active.
Check
Check setpoint, modulation band, manual/auto mode and any hold inputs; compare the controller’s pressure reading with a local gauge.

3Fuel limited at high fire

Points to it
Firing rate at 100% but fuel pressure sags at high fire; steam flow below rating.
Check
Trend fuel pressure at high fire against the burner’s required pressure.

4Burner trip or short cycling

Points to it
Burner status shows a lockout or frequent recycles at the start of the drop.
Check
Read the fault history and follow the flame-loss or airflow signature.

5Lost heat transfer

Points to it
Stack temperature higher than it used to be at the same firing rate; maximum output has fallen over months.
Check
Trend stack temperature at a fixed firing rate and O2; inspect tubes at the next shutdown. DOE notes that scale can reduce steam output if the firing rate cannot be raised to compensate.

How to read the trend

  1. Overlay three signalsSteam pressure, steam flow and firing rate on one chart, for the drop and a normal day.
  2. Ask whether it fired upIf the firing rate did not rise, look at control. If it was already at 100%, look at capacity, fuel and heat transfer.
  3. Rule out a tripCheck burner status and the fault history for a lockout at the start of the drop.
  4. Look at the long trendCompare stack temperature and maximum output with months ago.

Evidence to collect

Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.

Related