Fireye NX6300 (Nexus) fault F20: Drive position fault
A drive position fault means a fuel or air drive (servo, or fan VSD) was not where the commissioned profile says it should be. F20 is drive 0; the following numbers are the other drives. The controller checks the close and purge positions during start-up and the fuel/air ratio while firing, so the subset tells you whether the problem is mechanical, communication or inside the servo.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a keypad photo, the fault history or a parameter export from your Fireye NX6300 (Nexus). InduQT compares the evidence and suggests the next useful checks.
When it happens
- Status 05: proving closed positions
- Status 07: proving purge positions
- Status 08–15: pre-purge, ignition and post-purge, if a drive moves off its set point
- Status 16: modulation, if a drive leaves the commissioned curve
Reading the subset
| Subset | What it tells you |
|---|---|
| 000 to 016 | Burner status when the fault occurred (position error) |
| 032 to 048 | CANbus communication error; the display shows ERR1 under the drive name |
| above 64 | Internal servo fault; the display shows ERR2 to ERR7 under the drive name |
Where it sits in the burner
Supervised function: Firing-rate positioning.
| Component | Signals to look at | How it fails |
|---|---|---|
| Air damper, actuator and linkage | Air damper position, Firing rate | Damper or valve linkage slip; Actuator or feedback fault; Air/fuel ratio drift |
| Fuel valve actuator and linkage | Fuel valve position, Firing rate | Damper or valve linkage slip; Actuator or feedback fault; Air/fuel ratio drift |
| Controller communication network | Burner sequence state | Communication wiring fault; Electrical noise on signal wiring |
| Combustion air fan (FD / ID) | Combustion fan running, Combustion fan speed, Combustion air pressure, Fan motor current, Fan vibration | Fan motor or drive fault; Restricted combustion air path; Bearing wear or misalignment |
Likely causes and checks
1Linkage or damper binding (subset 000–016)
- Points to it
- Fault at purge or during modulation; actuator labours or stalls.
- Check
- Disconnect and stroke the damper or valve by hand (burner off, qualified personnel) to check for binding; check couplings for slip.
2Stored close or purge position no longer reachable
- Points to it
- Fault before the drives reach purge, after mechanical work or servo replacement.
- Check
- The manual’s troubleshooting table points to feedback potentiometers and motor micro-switches, then resetting close and purge positions in Commission Ratio mode.
3CANbus fault (subset 032–048, ERR1)
- Points to it
- ERR1 under the drive name; display slow or freezing.
- Check
- Check CANbus wiring, screens and termination to the servo.
4Servo internal fault (subset above 64, ERR2–ERR7)
- Points to it
- Repeats on the same servo.
- Check
- Replace the servo; a replacement servo invalidates profiles that used it (F64) until re-commissioned.
5Fan VSD outside its error band
- Points to it
- Fault on the VSD drive while modulating; VSD current-limiting or slow ramp.
- Check
- Check the VSD ramp times and that its own PID is disabled, as the manual’s inverter section describes.
Telling it apart
- Position faults are drive-specific: note the drive number (F20 = drive 0) and its subset.
- A profile that will not run at all after a servo change is F64, not a position fault.
Evidence to collect
- Fault number (which drive) and subset
- ERR code under the drive name, if shown
- Any recent servo, linkage or VSD work
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.