Industrial boiler flame failure: causes and diagnostic sequence
A flame failure means the burner control did not see a proven flame when it required one: during the pilot or ignition trial, during the main-flame trial, or while firing. The control shuts the fuel valves and normally locks out. The stage at which it happened is the most useful single clue.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.
Where it shows up
- A lockout message on the burner control or its display module, usually naming the sequence stage.
- A flame-failure alarm on the boiler HMI or plant DCS, often followed by low steam pressure alarms.
- A drop of the flame signal reading to zero in the control’s diagnostics.
Likely causes and how to tell them apart
1Ignition not established
- Points to it
- Failure only during the pilot or ignition trial; no flame signal at all during the trial.
- Check
- Observe the igniter spark and pilot through the sight glass during a trial; check ignition transformer output and electrode condition and gap per the burner manual.
2Fuel supply pressure drops at light-off
- Points to it
- Failure on the main-flame trial, or when other gas users start; low gas-pressure switch events near the trip.
- Check
- Record gas pressure at the burner train during a light-off; compare with the burner’s required inlet pressure.
3Air/fuel ratio wrong at low fire
- Points to it
- Unstable or lifting flame at light-off; trips after a combustion tune or linkage work.
- Check
- Have the burner combustion-tested at low fire; check damper and fuel-valve linkage for slip.
4Flame detector cannot see the flame
- Points to it
- Flame visible but the control reports a weak or zero flame signal; signal has been drifting down over weeks.
- Check
- Compare the flame signal with the control’s documented minimum; inspect and clean the scanner lens or flame rod and check its sighting.
5Flame lost during firing
- Points to it
- Trips while running, often at load changes or high fire.
- Check
- Trend fuel pressure, air flow and firing rate around the trip; look for a pressure dip or damper movement just before it.
Diagnostic sequence
- Read the lockout before resettingPhotograph the control display or fault history. Note the stage (pilot trial, main trial, run) and the flame signal value if shown.
- Place the trip in the sequenceIgnition-trial failures point to ignition, pilot fuel or detection; main-trial failures to the main fuel train and light-off air; running failures to fuel stability, air or detection.
- Check what changedRecent maintenance, tuning, fuel supply work, weather and load changes often line up with the first trip.
- Gather data around the tripFuel pressure, air flow or damper position, firing rate and flame signal for the minutes before and after.
- Test one cause at a timeUse the checks above in order of likelihood, and record what you find so the next trip can be compared.
Evidence to collect
- Photo of the lockout message and fault history
- Burner control make and model
- Flame detector type (UV, infrared or flame rod)
- Gas or oil pressure and firing-rate trend around the trip
- Recent maintenance or tuning
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.