Fireye NX6300 F11 False Flame at pre-ignition, what to check?
My Fireye NX6300 burner control is locking out with an F11 False Flame fault. It seems to happen specifically during the pre-ignition phase when the spark starts. What should I investigate first?
The Fireye NX6300 F11 False Flame fault indicates the controller detected a flame signal when no flame should be present, such as before, during, or after the burner cycle. This lockout occurs because the controller cannot distinguish between a real flame and a faulty signal. When this fault occurs specifically at pre-ignition, it often points to the flame detector seeing the ignition spark.
Likely causes and checks
1Detector seeing ignition spark
- Points to it
- The flame detector is picking up the ignition spark as a flame signal, causing the controller to register a 'false flame' during the pre-ignition phase.
- Check
- Re-sight the scanner so it cannot view the spark. Also, check the routing of both the scanner cable and the ignition cable to ensure proper separation.
2Failing UV tube or self-check detector
- Points to it
- A failing UV tube or self-check detector can generate a false flame signal even in a dark, cold furnace. This can sometimes be preceded by F66 events.
- Check
- With the burner off, cover the scanner. If a flame signal persists, it indicates a fault with the detector or its input.
3Fuel still burning after shutdown
- Points to it
- Residual fuel burning after the shutdown sequence can cause a flame signal when none is expected, particularly during post-purge or when the burner is off.
- Check
- Look into the furnace. If a flame is visible, close the manual fuel valves and have the safety shutoff valves tightness-tested. The valve leak test function (if fitted) can assist here.
4Noise pickup on the flame input
- Points to it
- Electrical noise can interfere with the flame input signal, leading to intermittent false flame readings, often coinciding with motor or ignition switching.
- Check
- Verify the screen termination of the scanner cable and ensure it is properly separated from power and ignition wiring.
Next check: Given that the F11 fault occurs specifically at pre-ignition when the spark starts, the most likely cause is the detector seeing the ignition spark. You should first re-sight the scanner to prevent it from viewing the spark and check the routing of both the scanner and ignition cables.
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