How much does it cost to fix Keston error code B 30?

Typical repair cost for the Keston B 30 fault is £150-350 including labour.

B 30 High

Keston B 30 Fault Code

Q: What does the Keston B 30 fault code mean?

Your boiler is struggling to move water around your heating system properly, causing it to overheat because the hot water isn't getting away from the heat exchanger fast enough.

Also written as B30 — same fault.

The Keston B 30 fault code means: your boiler is struggling to move water around your heating system properly, causing it to overheat because the hot water isn't getting away from the heat exchanger fast enough.. It appears on 3 Keston models in our database.

Technical description: Difference between flow and return temperatures too high. Check water circulation

Typical repair cost £150-350 (including labour)

Engineer required

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

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Keston models that show the B 30 fault code

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

Source

Keston B 30 fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

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