H12 Medium

Worcester Bosch H12 Fault Code

The Worcester Bosch H12 fault code means: your boiler is struggling to detect the temperature of your hot water cylinder, which means it may fail to heat your water properly.. It appears on 1 Worcester Bosch 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: Storage sensor cylinder sensor.
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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Worcester Bosch models that show the H12 fault code

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

Source

Worcester Bosch H12 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

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