Honeywell 7800 Series fault 14: High Fire Sw.
During PREPURGE the module drives the firing-rate motor to high fire so the furnace is purged with full air, and waits for the high fire switch to prove it. Fault 14 means that proof never arrived within the allowed time.
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
- PREPURGE, while driving to high fire
Where it sits in the burner
Supervised functions: Purge, Firing-rate positioning.
| Component | Signals to look at | How it fails |
|---|---|---|
| Low fire and high fire position switches | Low fire position switch, High fire (purge) position switch | Pressure or position switch out of adjustment; Damper or valve linkage slip; Welded, jumpered or miswired contact |
| Air damper, actuator and linkage | Air damper position, Firing rate | Damper or valve linkage slip; Actuator or feedback fault; Air/fuel ratio drift |
Likely causes and checks
1Actuator does not reach high fire
- Points to it
- Damper stops short of full open; motor hums or stalls.
- Check
- Watch the actuator and damper during PREPURGE; check the drive signal, linkage and any mechanical stop.
2High fire switch cam out of adjustment
- Points to it
- Actuator reaches full travel but the switch does not make; appeared after linkage or motor work.
- Check
- Table 3 describes holding the sequence at high fire with the Run/Test switch and confirming line voltage at the high fire switch input; adjust the cam to the burner maker’s setting.
3Linkage slip between actuator and damper
- Points to it
- Switch makes but air flow at purge is low, or damper position does not match the actuator shaft.
- Check
- Mark the shaft and damper and check for slip at couplings and set screws.
Telling it apart
- Fault 14 is high fire not proven in PREPURGE; fault 20 is low fire not proven before ignition.
- If the actuator moves but no switch ever makes, compare both switches: a wiring fault often affects both.
Evidence to collect
- Code 14 and sequence status
- Actuator model and whether it reached full travel
- Any recent linkage or actuator work
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.