A05
Fondital
Flue Gas Exhaust / Air Pressure Fault
Boiler displays A05, fan runs but burner does not ignite, sometimes accompanied by whistling or wind noise
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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
Blocked or restricted Fondital concentric flue, Faulty air pressure switch, Damaged or disconnected flue fan pressure tubing, Defective fan motor
How to Fix / Troubleshooting
Safety: A flue fault can lead to dangerous combustion products. Do not attempt to dismantle the flue yourself. Switch off the boiler and ventilate the room.
User checks:
- Flue terminal: From outside, visually check that the flue terminal is not blocked by leaves, nests, snow, or objects. Do not insert tools into the terminal.
- Ventilation: Ensure any ventilation grilles in the boiler room are unobstructed.
- Reset: Try a single reset. If A05 returns, call a qualified technician.
Technician actions:
- Inspect and clean the Fondital concentric flue system and check for correct installation and slope.
- Test the air pressure switch and silicone tubes for blockage, cracks, or disconnection.
- Measure voltage and operation of the flue fan motor; replace if noisy, seized, or out of spec.
- Verify correct operation of the main PCB fan control circuit.
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Repair Difficulty
Hard
4/5
Required Part
Air Pressure Switch
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