Honeywell 7800 Series fault 16: Flame-Out Timer
During the Pilot Flame Establishing Period (PFEP) the module energises the igniter and pilot valve and expects the flame detector to prove a pilot flame before the period ends. Fault 16 means the period expired without a usable flame signal, so 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), the pilot trial for ignition
Where it sits in the burner
Supervised functions: Ignition and pilot, Flame supervision.
| Component | Signals to look at | How it fails |
|---|---|---|
| Ignition transformer and electrode | Ignition output | Igniter electrode wear or wrong gap; Ignition transformer or lead failure |
| Pilot gas train | Pilot valve output, Pilot gas pressure | Fuel valve not opening fully; Regulator out of adjustment or sticking; Fuel supply pressure droop |
| 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 |
| Air damper, actuator and linkage | Air damper position, Firing rate | Air/fuel ratio drift; Damper or valve linkage slip; Actuator or feedback fault |
Likely causes and checks
1No spark or a weak spark
- Points to it
- No ignition sound or visible spark through the sight glass.
- Check
- Inspect the electrode tip, insulator and gap; check the transformer output and high-voltage lead per the burner manual.
2Pilot gas not arriving
- Points to it
- Spark present but no pilot flame; pilot regulator or valve recently serviced.
- Check
- Read pilot gas pressure during the trial; confirm the pilot valve opens and the manual pilot cock is open.
3Detector does not see the pilot
- Points to it
- Pilot visible but flame signal stays below the minimum.
- Check
- Measure the flame signal at the test jack during the pilot trial. 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). Clean and re-sight the scanner, or check flame rod position.
4Amplifier and detector not compatible
- Points to it
- After a detector or amplifier was replaced.
- Check
- Confirm the plug-in amplifier type matches the detector, as Table 3 directs.
5Too much light-off air
- Points to it
- Pilot lights then blows out; after damper or low-fire position work.
- Check
- Check the light-off damper position against the commissioning record.
Telling it apart
- Faults 16 and 28 both point at the pilot trial. The checkout publication’s “failure to ignite pilot” safety test is documented as producing fault 28; use the same spark → pilot fuel → detection split for either.
- If the pilot proves but the burner trips once the main valve opens, the code becomes 19.
Evidence to collect
- Code 16 and sequence status (PILOT IGN)
- Flame signal (Vdc) during the pilot trial
- Pilot gas pressure during the trial
- Detector and amplifier model numbers
- Observation of spark and pilot through the sight glass
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.