8 + Medium

Biasi 8 + Fault Code

Also written as 8 — same fault.

The Biasi 8 + fault code means: your boiler's outside temperature sensor has failed, meaning the system doesn't know how hard it needs to work to heat your home based on the weather.. It appears on 2 Biasi models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: External NTC probe failure.
Typical repair cost £90-160 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Biasi models that show the 8 + fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Biasi 8 + fault code information on this page is sourced and cross-checked against the official Biasi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026