F27
Glow-worm
Flame Detection Error / False Flame Signal
Boiler displays F27, indicating aborted ignition, which may occur with an incorrect gas type or contamination.
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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
Moisture or contamination on the electrode, Electrical noise or interference, Incorrect earthing, PCB flame circuit fault
How to Fix / Troubleshooting
Safety: Isolate the power and gas supply before internal inspection.
- Power reset: Turn off the power for several minutes, then restore. If F27 persists, internal checks are needed.
- Engineer tasks:
- Inspect and clean the ignition/ionisation electrode and ceramic insulator.
- Check earth bonding and wiring layout to minimise interference.
- Verify the correct gas type and injector for the installation.
- Test the PCB flame detection circuitry and replace the PCB if necessary.
False flame detection must be resolved to ensure safe ignition control.
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Repair Difficulty
Professional Required
5/5
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