Field Troubleshooting Question (Burner Control System – Pilot Burner Sequence Failure) The boiler burner management system fails to complete the pilot burner activation procedure. The pilot solenoid opens, but the flame does not ignite, and the system locks out with “Pilot Flame Fail.” What are the most likely reasons, and what diagnostic measures should a technician take to identify the problem?
A burner control system failing to create a pilot flame during the ignition phase is a common field problem that causes numerous lockouts. When the pilot solenoid opens but no flame is detected, the issue is most likely with fuel supply, ignition energy, or flame detection. Begin by checking the fuel supply to the pilot burner. A partially blocked pilot nozzle, low gas pressure, air in the line, or a stuck pilot solenoid can all cause improper fuel delivery. Check that the pilot gas regulator is working and that the pressure is within the burner manufacturer’s recommended range. Next, check the ignition source. For spark ignition systems, check the igniter rod for carbon deposits, cracks, or misalignment with the pilot flame zone. Weak sparks, defective ignition cables, and faulty ignition transformers can all disrupt the process. In oil-fired systems, inspect the atomization quality and ensure proper air-fuel mixing. If the ignition side is confirmed to be good, test the flame detecting equipment. Even if the pilot is quickly ignited, the controller may fail flame verification due to a dirty or misaligned UV/IR sensor, poor flame intensity, or wiring difficulties. Inspect the scanner’s viewing port for soot buildup and ensure correct grounding and signal strength.
Finally, examine the burner management system (BMS) logic, interlocks, and permissives. Low airflow, purging faults, and limit switch failures can all prohibit the pilot from keeping powered on. Before restarting the burner, perform a step-by-step verification to ensure that the underlying cause has been accurately identified.