F9
Glow-worm
PCB / internal control fault
F9 error, furnace will not fire, may occur after power surge or wiring work
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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
Damaged Glow-worm main PCB, Incorrect polarity or missing earth, Loose multi-pin connectors, Overvoltage or surge damage
How to Fix / Troubleshooting
Safety: Isolate the appliance from the mains. Electronic work must be done by a competent person.
Checks:
- Verify correct mains polarity, voltage, and earth at the appliance terminals using a multimeter.
- Inspect all PCB connectors for secure fit and signs of overheating or burning.
- Reset the appliance once after confirming supply is correct.
Technician actions:
- Visually inspect the PCB for burnt tracks, swollen capacitors, or water damage.
- Check low-voltage outputs to sensors and actuators according to Glow-worm service data.
- If PCB is confirmed faulty and all external components test OK, replace the main control board with the correct Glow-worm part and transfer any configuration links or jumpers as specified.
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Repair Difficulty
Professional Required
5/5
Required Part
Main Control PCB
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