121 Medium

Worcester Bosch 121 Fault Code

The Worcester Bosch 121 fault code means: your boiler's solar water heating system is struggling because the water-circulating pump is physically stuck and unable to move fluid around the system.. 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: Solar pump (SP) sticking due to physical blockage.
Typical repair cost £150-250 (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 121 fault code

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

Source

Worcester Bosch 121 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 7 July 2026