4.12 Medium

Keston 4.12 Fault Code

Also written as 412 — same fault.

The Keston 4.12 fault code means: your boiler is providing central heating as expected, but it is failing to heat your domestic hot water, likely due to a sensor or valve getting stuck in the wrong position.. It appears on 1 Keston model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: NO HW BUT CH ON
Typical repair cost £150-300 (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 4.12 fault code

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

Source

Keston 4.12 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 7 July 2026