BoilerFaultCodesWorcester Bosch B7 257 Fault Code
Also written as B7257 — same fault.
The Worcester Bosch B7 257 fault code means: your boiler's computer brain has encountered an internal software or hardware error and is struggling to communicate with the rest of the system.. It appears on 12 Worcester Bosch models in our database.
Technical description: Internal error – possible control board problem
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the B7 257 fault code
Click a model for the full fault code list and model-specific repair notes.
- 24 RSF Repair: £280-550
- 26 CDi Xtra Repair: £280-450
- 30i Junior Repair: £280-450
- 35 RSF Repair: £280-550
- Danesmoor Repair: £280-550
- Greenstar 12i System Repair: £150-350
- Greenstar 12i System Repair: £250-450
- Greenstar i Repair: £250-450
- Heatslave Repair: £350-£580
- Hideaway Repair: £250-£450
- Junior 24i Repair: £280-£450
- Junior 28i Repair: £280-450
Source
Worcester Bosch B7 257 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