What does the Keston B 25 fault code mean?

Your boiler is overheating because water isn't moving through the system fast enough, likely due to trapped air or a blockage in your pipes.

How much does it cost to fix Keston error code B 25?

Typical repair cost for the Keston B 25 fault is £120-250 including labour.

Flow temperature climbing too quickly. Possible air lock or circulation blockage

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Almost always a stuck diverter valve on combis.

Each noise points to a different fault.

Lockout fault with a reset-needed pattern.