05
Biasi
Air Pressure Switch Not Proving
Boiler shows error 05, no heating or hot water, fan may run but no ignition sequence completes.
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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 air pressure switch, Blocked or incorrectly installed flue, Blocked venturi or fan outlet, Split or disconnected pressure tubing
How to Fix / Troubleshooting
Safety: Isolate power and gas. Flue and combustion checks must be done by a qualified engineer.
- Check flue terminal externally: Ensure the Biasi flue outlet is not blocked by grills, covers, or debris.
- Inspect condensate system: A blocked or frozen condensate pipe can cause backpressure. Thaw frozen sections with warm (not boiling) water and clear any blockages.
- Visual check of pressure tubes: With the case removed, inspect the silicone tubes from the fan/venturi to the air pressure switch. Refit any loose tubes and replace if perished or split.
- Engineer tests: A technician should test continuity and switching of the air pressure switch with a multimeter, verify correct flue length and configuration, and clean the venturi if partially blocked.
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Repair Difficulty
Professional Required
5/5
Required Part
Air Pressure Switch
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