Fireye NX6100 F66 Flame Test Failed, subset 1: what to check?

Question

My Fireye NX6100 controller is showing an F66 fault with subset 1. This happens during firing, and I've seen F11 events before. What should I check first?

Top answer · Written by InduQT from the fault guide and manufacturer manuals cited below · Oct 28, 2026

The Fireye NX6100 F66 fault, "Flame Test Failed," means the controller's regular self-check of its flame input failed. This test ensures the flame input reads "no flame" when it should, using either a scanner shutter or the detector's self-check mechanism. A failing UV tube or a stuck shutter can cause this, leading the controller to distrust the flame input.

Likely causes and checks

1UV tube failing or shutter stuck

Points to it: The controller's flame input test failed because the UV tube is no longer functioning correctly or the scanner's shutter is stuck, preventing the 'no flame' signal from being registered. This is indicated by Subset 1 and may be preceded by F11 events.
Check: Test the scanner outside the burner as directed by the manual. If the dark check still fails, replace the scanner.

2Flame input wiring short

Points to it: A short in the flame input wiring can cause the controller to incorrectly detect a flame signal during its self-check, leading to an F66 fault. This is indicated by Subset 3 and often occurs after wiring work or if the cable has been damaged.
Check: Inspect the scanner cable and its terminals for any signs of shorts.

3Self-check detector fault

Points to it: If the flame detector itself has an internal fault or memory issue, its self-check function may fail, triggering the F66 fault. This is indicated by Subsets x02–x06.
Check: The manual directs replacing the detector for memory or internal faults.

4CANbus to the detector

Points to it: Problems with the CANbus communication link to the flame detector can prevent the controller from properly executing or receiving the results of the flame input test. This is indicated by Subset x01.
Check: Check the CANbus wiring connecting to the detector for any issues.

Next check: Given the subset 1 and prior F11 events, the most likely cause is a failing UV tube or a stuck shutter. You should test the scanner outside the burner as directed by the manual and replace it if the dark check still fails.

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.