Honeywell 7800 Fault 28: Pilot Flame Failure

Question

My industrial burner control, a Honeywell RM7800, is throwing a Fault 28. The pilot valve opens, but the pilot never lights, and the main valves never open. What should I check first?

Top answer · Written by InduQT from the fault guide and manufacturer manuals cited below · Oct 27, 2026

Fault 28 indicates a pilot flame failure on a Honeywell 7800 Series relay module. This occurs during the PILOT IGN (PFEP) stage, 4 or 10 seconds after the pilot valve opens, and prevents the main valves from opening. The most common causes include issues with the pilot valve, incorrect pilot pressure, ignition problems, or detector/sighting issues.

Likely causes and checks

1Pilot pressure wrong

Points to it: Incorrect pilot pressure can lead to a small, lazy, or lifting pilot flame, which the system may not detect as stable. This often occurs after recent regulator adjustments.
Check: Measure the pilot pressure and repeat the pilot turndown test as described in the checkout publication.

2Ignition problem

Points to it: A lack of spark or a spark occurring in the wrong location will prevent the pilot from igniting.
Check: Examine the ignition transformer and the electrode for any faults or damage.

3Detector or sighting

Points to it: Even if a pilot flame is visible, a low flame signal indicates that the detector is not properly sensing the flame or is incorrectly sighted.
Check: Verify the detector sighting and check the amplifier. The minimum reliable flame signal for a pilot or main flame on the 7800 test jack is 1.25 Vdc.

Next check: If the pilot proves and the trip follows main valve opening, the fault code would be 19, not 28.

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.