Fireye NX6100 (Nexus) troubleshooting
The Fireye NX6100 is a Nexus integrated controller that combines flame safeguard, burner sequencing and parallel fuel/air positioning. It shares the Nexus fault numbering with the NX6300 but supports more drives and inputs, and adds faults for a second air switch, valve proof of closure and gas pressure supervision.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.
How it reports faults
- Each fault number has a prefix: F means the fault occurred and is still present, C means it occurred and has cleared, L means a programmed limit was exceeded.
- Many faults cause a non-volatile lockout that survives a power cycle; some faults and limits only raise a warning.
- Most faults carry a subset read on the Engineer’s Key screen. Subsets are bit sums (1, 2, 4 … 128) or, for flame and air faults, the burner status number.
- The 2-line text display stores the last 128 events and faults; the touchscreen display stores thousands. ComFire2 software shows the full set.
Operating sequence
- 00 Non-volatile lockoutFuel valves off, alarm on until muted; stays locked out until faults clear.
- 01–02 Burner off, wait for purgeValves proven closed, no flame and no air pressure; waits for burner select and a profile.
- 03–05 Leak test and prove closedOptional gas valve leak test starts; drives move to closed and are compared with commissioned positions.
- 06–08 Prove air, purge positions, pre-purgeFan starts; air pressure must be proven after t1; drives reach purge positions and pre-purge t2 runs.
- 09–10 Ignition position, pre-ignitionDrives move to ignition positions; igniter energised for t3.
- 11–12 Pilot ignitionPilot valve opens; flame must be proven by the end of safety time t4.
- 13–14 Main ignitionMain valves open for safety time t6, then the main flame interval t7; flame and air must stay proven.
- 15–16 Low fire, modulationLow fire hold t8, then modulation on demand with flame and air supervised.
- 17–18 Post-purgeFuel closes; air drives move to post-purge before returning to 01.
Fault codes
| Code | Name |
|---|---|
| F10 | Flame Failure |
| F11 | False Flame |
| F14 | Combustion air pressure not detected |
| F15 | Combustion air pressure detected when it should not be |
| F20 | Drive position fault |
| F41 | Boiler sensor fault or safety limit exceeded |
| F42 | Valve prove (leak) test fault |
| F64 | Profile Invalid |
| F66 | Flame Test |
| F16 | Second (primary) air pressure not detected |
| F30 | Gas Proof of Closure fault |
| F43 | Gas pressure limit exceeded, or sensor fault |
| F01–F09 | External alarm from low-voltage inputs 1 to 9 |
| F12–F13 | External alarm from high-voltage input 12 or 13 |
| F17 | Optional second (primary) air pressure detected when it should not be |
| F18 | Not enough set points entered in the profile |
| F19 | Circuit board voltage reference fault |
| F20–F29 | Drive 0 to 9 position fault |
| F31 | Oil proof of closure fault |
| F32 | Safety input fault (low-voltage inputs) |
| F33 | Burner input fault (high-voltage inputs) |
| F34 | Primary relay fault |
| F35 | ADC fault |
| F36 | Reset fault: too many resets with no fault present |
| F37–F39 | RAM, program memory or profile table check failed |
| F40 | Single fuel only fault: profile fuel not available on this unit |
| F45 | Low cup speed |
| F46 | EEPROM memory check failed |
| F50 | Oxygen probe heater fault |
| L52–L53 | Oxygen low or high limit alarm |
| F54 | Oxygen probes mismatch, or CO high limit |
| L55 | Trim limit alarm |
| F57 | Auto trim commissioning fault |
| L58–L59 | Flue temperature low or high alarm |
| F61 | Air pressure level fault |
| F63 | Option parameters uploaded: check and confirm |
| F65 | Power-up lockout |
| F67–F69 | Secondary relay, program memory or watchdog fault |
| F70–F79 | User faults from the programmable logic |
| L89 | FGR input fault |
Evidence to collect
- Photo of the fault with its F/C/L prefix
- Subset from the Engineer’s Key screen
- The event log around the lockout
- Flame scanner type and signal
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.