Honeywell RM7800 Fault 33 after shutdown, what to check?
I'm getting a Fault 33 on my Honeywell RM7800 burner control module right after a shutdown. The pre-ignition interlock isn't proving, and I'm not sure where to start troubleshooting.
Fault 33 on a Honeywell RM7800 series relay module indicates a pre-ignition interlock issue, specifically that the proof-of-closure switch on the safety shutoff valves did not prove closed when required. This prevents the system from confirming the fuel valves are shut before proceeding to purge or ignition. It typically occurs during STANDBY, PREPURGE, or after the first five seconds of POSTPURGE during a safety shutdown test.
Likely causes and checks
1Valve closing slowly
- Points to it
- The safety shutoff valve is not closing within the required five-second timeframe, preventing the proof-of-closure switch from activating in time.
- Check
- Time the valve's closing sequence. If it exceeds five seconds, service or replace the valve actuator.
2Proof-of-closure switch out of adjustment or failed
- Points to it
- The valve may be closing fully, but the proof-of-closure switch is either misadjusted or faulty, failing to make contact and signal its closed position to the module.
- Check
- Inspect the proof-of-closure switch contacts and adjust it according to the valve manufacturer's specifications. Confirm line voltage (120 Vac) is present at the pre-ignition interlock input when the system is in STANDBY.
Next check: Begin by timing how long it takes for the safety shutoff valve to close after a shutdown. If it's taking longer than five seconds, focus on the valve actuator. Otherwise, inspect the proof-of-closure switch and its wiring.
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