811 Medium

Worcester Bosch 811 Fault Code

The Worcester Bosch 811 fault code means: your boiler has failed to reach the high temperature required to kill potential bacteria in your hot water supply, so it is alerting you that the water may not be safe for certain uses.. 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: Hot water heating: thermal disinfection failed
Typical repair cost £120-250 (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 811 fault code

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

Source

Worcester Bosch 811 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