Honeywell 7800 Series fault 28: Pilot Flame Fail
Fault 28 means the pilot flame failed. In Honeywell’s own safety shutdown test, a pilot that cannot light produces fault 28 four or ten seconds after the pilot valve opens, depending on the PFEP jumper setting. The main valves never opened.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a keypad photo, the fault history or a parameter export from your Honeywell 7800 Series. InduQT compares the evidence and suggests the next useful checks.
When it happens
- PILOT IGN (PFEP), 4 or 10 seconds after the pilot valve opens depending on the PFEP jumper
Where it sits in the burner
Supervised functions: Ignition and pilot, Flame supervision.
| Component | Signals to look at | How it fails |
|---|---|---|
| Pilot gas train | Pilot valve output, Pilot gas pressure | Regulator out of adjustment or sticking; Fuel valve not opening fully; Fuel supply pressure droop |
| Ignition transformer and electrode | Ignition output | Igniter electrode wear or wrong gap; Ignition transformer or lead failure |
| Flame scanner (UV / IR) | Flame signal | Scanner no longer sighted on the flame root; Dirty or fogged scanner sight path; Detector or amplifier ageing; Electrical noise on signal wiring |
| Flame amplifier / flame input | Flame signal | Wrong detector, amplifier or configuration; Detector or amplifier ageing; Electrical noise on signal wiring |
Likely causes and checks
1Pilot valve not opening
- Points to it
- No pilot flame and no change in pilot pressure when the valve is energised.
- Check
- Check pilot valve wiring and that the valve actuates; Table 3 lists this first.
2Pilot pressure wrong
- Points to it
- Small, lazy or lifting pilot; regulator recently adjusted.
- Check
- Measure pilot pressure and repeat the pilot turndown test from the checkout publication.
3Ignition problem
- Points to it
- No spark, or spark in the wrong place.
- Check
- Inspect the ignition transformer and electrode.
4Detector or sighting
- Points to it
- Pilot visible but flame signal low.
- Check
- Check detector sighting and amplifier. The checkout publication uses 1.25 Vdc as the minimum flame signal for a reliable pilot or main flame on the 7800 test jack (65-0229-2, Flame signal and pilot turndown tests).
Telling it apart
- See fault 16, which also points at the pilot trial.
- If the pilot proves and the trip follows main valve opening, the code is 19.
Evidence to collect
- Code 28 and sequence status
- PFEP jumper setting (4 or 10 s)
- Pilot gas pressure and flame signal during the trial
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.