How much does it cost to fix Ferroli error code B-4?

Typical repair cost for the Ferroli B-4 fault is £120-220 including labour.

B-4 High

Ferroli B-4 Fault Code

Q: What does the Ferroli B-4 fault code mean?

Your boiler has stopped working because it cannot correctly detect the water temperature or believes the internal system is becoming dangerously hot.

Also written as B4 — same fault.

The Ferroli B-4 fault code means: your boiler has stopped working because it cannot correctly detect the water temperature or believes the internal system is becoming dangerously hot.. It appears on 2 Ferroli models in our database.

Technical description: Central heating sensor (34) not connected or boiler temperature too high or boiler thermostat (61) below CH temperature

Typical repair cost £120-220 (including labour)

Engineer required

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

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Ferroli models that show the B-4 fault code

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

Source

Ferroli B-4 fault code information on this page is sourced and cross-checked against the official Ferroli service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026