How much does it cost to fix Biasi error code 4 +?

Typical repair cost for the Biasi 4 + fault is £100-£280 including labour.

4 + High

Biasi 4 + Fault Code

Q: What does the Biasi 4 + fault code mean?

Your boiler has stopped working because the water pressure is either too low, too high, or the water isn't moving through the system correctly.

Also written as 4 — same fault.

The Biasi 4 + fault code means: your boiler has stopped working because the water pressure is either too low, too high, or the water isn't moving through the system correctly.. It appears on 2 Biasi models in our database.

Technical description: Pump circulation failure, insufficient system pressure or pressure above 3 bar, water pressure sensor not connected.

Typical repair cost £100-£280 (including labour)

DIY fix possible

Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.If the pressure is below 1 bar, use the filling loop underneath the boiler to carefully top it up.If the pressure is above 3 bar, bleed a radiator to release excess pressure.Restart the boiler once the pressure is corrected.

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Biasi models that show the 4 + fault code

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

Source

Biasi 4 + 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 27 April 2026