03
Biasi
Fan / Air Pressure Switch Fault
Boiler shows error 03, fan does not start or stops quickly, no ignition attempt.
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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
Faulty fan motor, Blocked flue or condensate in flue, Faulty air pressure switch, Damaged or blocked air pressure tubing
How to Fix / Troubleshooting
Safety: Switch off power and isolate gas. The flue system is part of the combustion circuit; only a competent engineer should dismantle it.
- Listen for fan operation: On a heat demand, you should hear the fan start before ignition. If silent, suspect the fan or PCB.
- Check flue terminal: From outside, ensure the Biasi flue terminal is clear of obstructions and not submerged in snow or blocked by covers.
- Inspect condensate: Check that the condensate trap and pipe are not blocked or frozen, as this can cause backpressure in the flue and prevent the air pressure switch from proving.
- Visual check of fan and tubing: With the case off, inspect the fan for signs of overheating or seized bearings. Check the silicone tubes from the fan/venturi to the air pressure switch for splits, kinks, or water inside.
- Engineer tests: A technician should test the fan supply voltage from the PCB, verify the air pressure switch operation with a manometer, and confirm that the flue is correctly installed to Biasi specifications.
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Repair Difficulty
Professional Required
5/5
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