Medium
811 on Worcester Bosch Greenstar 4000

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Engineer required

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

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