Flame failure fault during run

Filter loading is a primary cause of flame failure faults during run, not a marginal one. The mechanism: the burner needs design airflow across it to hold a stable flame and a correct fuel/air ratio. When AMU pre-filters or intake filters load past their change cycle, airflow drops, the differential pressure over the burner shifts, and the air pressure safety trips the burner out or cycles it constantly. The weakened airstream also lets the flame burn erratic and lift off the flame sensor, so the control board sees no-flame even while gas is flowing.

Two filter habits prevent this fault. First, routine changes. Run past cycle and you are also running a rich fuel/air mixture, which raises carbon monoxide in and around the booth (a worker-exposure hazard with hard regulatory limits) and fatigues the burner itself, rotting and cracking baffles and mixers years early. Second, correct spec. The burner was commissioned against the pressure drop of specific media; swapping in cheaper filters or a different MERV or CFM rating changes the airflow balance the same way loading does and produces the same faults. Replace with what the booth was designed and commissioned with.

If AMU and intake media are fresh, on spec, and the manometer reads at the commissioned baseline, the filter explanation is ruled out and the diagnostic is combustion-side.

The compliance exposure here is carbon monoxide. A burner running a rich fuel/air mixture from starved airflow raises CO, and workplace CO exposure is regulated with hard limits. NFPA 33 treats burner flame supervision and its safety interlocks as life-safety controls in a spray environment, so an air pressure safety that keeps tripping is a signal to fix airflow, never something to bypass. Repeated flame-failure events also degrade cure-cycle quality downstream. Do not accept intermittent flame failure as normal, and never jumper a safety to keep a booth running.