Honeywell 7800 Series fault 33: Pre-Ignition ILK
The pre-ignition interlock is usually the proof-of-closure switch on the safety shutoff valves. Fault 33 means the module did not see it proven when required, so it cannot confirm the fuel valves are shut before purge or ignition.
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
- STANDBY or PREPURGE
- After the first five seconds of POSTPURGE (safety shutdown test)
Where it sits in the burner
Supervised function: Valve proving and proof of closure.
| Component | Signals to look at | How it fails |
|---|---|---|
| Main safety shutoff valves | Main fuel valve output, Valve proof of closure | Valve seat leakage or slow closing; Fuel valve not opening fully; Welded, jumpered or miswired contact |
Likely causes and checks
1Valve closing slowly
- Points to it
- Fault appears just after a shutdown; valve actuator sluggish.
- Check
- Table 3 states the valve must close within five seconds; time the valve closing and service or replace the actuator.
2Proof-of-closure switch out of adjustment or failed
- Points to it
- Valve closes fully but the switch does not make.
- Check
- Check the POC switch contacts and adjustment per the valve maker; confirm line voltage at the pre-ignition interlock input in STANDBY.
Telling it apart
- Fault 10 is the pre-ignition interlock fault reported during STANDBY on RM7800, 7840 and 7838B; fault 68 is the equivalent on EC/RM7810, 7820, 7830 and 7850.
Evidence to collect
- Code 33 and sequence status
- Valve and actuator model, POC switch type
- Measured valve closing time
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.