BoilerFaultCodesWorcester Bosch Fb Fault Code
Also written as FB — same fault.
The Worcester Bosch Fb fault code means: your boiler has shut itself down as a safety precaution because it detected a possible problem with the gas supply, so please don't try to reset it repeatedly and arrange for a gas safe registered engineer to check it promptly.. It appears on 9 Worcester Bosch models in our database.
Technical description: Gas valve EV1 leak test failed
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A cover plan would handle faults like Fb: no call-out fees, no surprise bills.
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Worcester Bosch models that show the Fb fault code
Click a model for the full fault code list and model-specific repair notes.
- 533 Compact Repair: £180-350
- 535 Compact Repair: £180-350
- Greenstar 25 Si Compact Repair: £250-450
- Greenstar 25Si Compact ErP Repair: £250-450
- Greenstar 27i System Compact ErP Repair: £250-450
- Greenstar 30 Si Compact Repair: £250-450
- Greenstar 30i System Compact ErP Repair: £250-450
- Greenstar 30Si Compact ErP Repair: £250-450
- Greenstar CDi Compact Repair: £200-350
Source
Worcester Bosch Fb fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch 535 Compact manual (PDF)
- Worcester Bosch Greenstar 30 Si Compact manual (PDF)
- Worcester Bosch Greenstar 30Si Compact ErP manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026