How much does it cost to fix Keston error code 9 (w/ flashing b)?

Typical repair cost for the Keston 9 (w/ flashing b) fault is £150-300 including labour.

9 (w/ flashing b) High

Keston 9 (w/ flashing b) Fault Code

Q: What does the Keston 9 (w/ flashing b) fault code mean?

Your boiler has detected that it is getting too hot or does not have enough water inside, so it has safely shut itself down to prevent damage.

Also written as 9WFLASHINGB — same fault.

The Keston 9 (w/ flashing b) fault code means: your boiler has detected that it is getting too hot or does not have enough water inside, so it has safely shut itself down to prevent damage.. It appears on 1 Keston model in our database.

Technical description: Overheat or water pressure lockout

Typical repair cost £150-300 (including labour)

Engineer required

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

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Keston models that show the 9 (w/ flashing b) fault code

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

C55 Repair: £150-300

Source

Keston 9 (w/ flashing b) 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