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Flame loss while firing: 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.

A flame loss while firing ends the same way every time: the flame signal drops below the control’s threshold and the burner locks out. What differs is what moved first. Looking at the minutes before the trip, in the order the signals changed, usually separates a fuel problem from an air, ratio or detection problem faster than any single alarm.

Illustrative pattern · simulated, not plant data

Firing rateMain gas pressureFlame signalLockout
Fuel-pressure variant: gas pressure sags as the burner ramps toward high fire; the flame signal collapses seconds later.
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.

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Where it shows up

Signals to trend

SignalWhat it does in this failure
Flame signalFalls to zero at the trip. A slow decline over days or weeks before the first trip points to detection; a sudden drop from a normal value means the flame really went out or the signal path broke.
Main gas pressureIf it sags in the seconds before the flame signal drops, the fuel supply is the lead suspect.
Firing rateA trip that follows a step in firing rate points to the fuel/air curve or supply capacity at that rate.
Air damper positionA damper that moves without a matching fuel valve move suggests linkage slip or a servo fault.
Flue gas oxygenA jump in O2 just before the trip suggests a lean flame blow-off; low O2 with CO suggests a rich, unstable flame.
Combustion air pressureIf air pressure falls first, follow the combustion airflow signature instead.

Variants: what moves first, and what it points to

1Detection decay

Points to it
Flame signal drifts down over days or weeks; on the day of the trip, fuel, air and firing rate are steady.
Check
Clean the scanner sight path and confirm sighting at low and high fire; compare the flame signal with the control’s documented minimum.

2Fuel pressure sag

Points to it
Gas (or oil) pressure dips first, often as the burner ramps up or another user starts; the flame signal collapses within seconds.
Check
Trend burner fuel pressure through a ramp to high fire; check regulator response and supply capacity.

3Ratio upset at a firing-rate change

Points to it
Trip follows a firing-rate step; O2 swings before the flame signal falls.
Check
Combustion-test at the firing rate where trips happen; check linkages and servo positions against the commissioned curve.

4Signal-path noise

Points to it
Short drop-outs of the flame signal with no change in fuel, air or firing rate, sometimes coinciding with motor starts.
Check
Check scanner cable routing, screens and terminations.

How to read the trend

  1. Line up the tripExport flame signal, fuel pressure, firing rate, damper position and O2 for 10 minutes either side of the trip, at the fastest sample rate available.
  2. Find what moved firstMark the first signal to leave its normal band before the flame signal dropped.
  3. Check the historyCompare the flame signal at the same firing rate over the last weeks; a slow decline is a different problem from a sudden loss.
  4. Match to the variantUse the variants above to choose the first physical check.

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.

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