F64
Glow-worm NTC Sensor / PCB Analogue Fault

Boiler displays F64, sensor or PCB temperature input error

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Multiple NTC sensors reading out of range, PCB analogue circuit failure, Wiring harness fault, Short between sensor lines

How to Fix / Troubleshooting

Safety: Isolate power before testing sensors.

  • Reset: Perform a reset. If F64 returns, internal diagnostics are needed.
  • Engineer tasks:
    • Measure resistance of all NTC sensors (flow, return, DHW, flue if fitted).
    • Check wiring harness for shorts or damage.
    • Replace faulty sensors or main PCB as indicated.

Do not bypass sensors; they are essential for safe operation.

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Repair Difficulty

Hard 4/5

Required Part

Flow NTC Temperature Sensor
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