BoilerFaultCodesWorcester Bosch b1 Fault Code
Also written as B1 — same fault.
The Worcester Bosch b1 fault code means: your boiler's main control chip is either loose or has failed, which means the computer can't identify the specific model to operate safely.. It appears on 37 Worcester Bosch models in our database.
Technical description: Keyed plug not detected.
What causes the Worcester Bosch b1 fault?
This fault occurs when the small memory chip, known as a code plug, becomes loose or fails, meaning the boiler's main computer can no longer identify which model it is controlling. Without this vital identity information, the boiler shuts down immediately as a safety precaution because it doesn't know its own operating limits. The most common cause is either a vibration-related loose connection or an internal electronic failure within the plug or the main circuit board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A cover plan would handle faults like b1: no call-out fees, no surprise bills.
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Worcester Bosch models that show the b1 fault code
Click a model for the full fault code list and model-specific repair notes.
- 532 / 537 / 542 Repair: £150-300
- 537i Repair: £150-300
- Bosch Greenstar ZWBR 7-25A
- CDi Classic Repair: £90-180
- CDi Classic Regular Repair: £150-300
- CDi Highflow Repair: £150-250
- Greenstar 2000 Repair: £150-250
- Greenstar 24
- Greenstar 24i / 28i Junior Repair: £150-300
- Greenstar 25 Si Repair: £120-250
- Greenstar 25CDi Repair: £150-250
- Greenstar 25HE Repair: £120-350
- Greenstar 25i (ZWB 7-25) Repair: £150-250
- Greenstar 28
- Greenstar 30 CDi System
- Greenstar 30CDi Classic System ErP Repair: £120-280
- Greenstar 30HE Repair: £120-450
- Greenstar 30si Repair: £120-250
- Greenstar 35 CDi range Repair: £120-250
- Greenstar 42CDi Repair: £90-180
- Greenstar CDi Classic (2012) Repair: £100-250
- Greenstar CDi Compact Repair: £120-350
- Greenstar Highflow Repair: £90-180
- Greenstar i Repair: £120-£250
- Greenstar R 28 HE System Repair: £90-180
- Greenstar R29 40 HE Repair: £120-250
- Greenstar System Repair: £150-300
- Greenstar ZWB7 Repair: £120-250
- Heatslave Repair: £120-280
- Highflow 400 Electronic BF
- Highflow 440 CDi Repair: £90-180
- Highflow 550 CDi Repair: £90-180
- Highflow CDi Repair: £150-250
- R30 HE Plus Repair: £90-180
- Worcester 25/30 HE Repair: £120-350
- ZB 7 27 HE Repair: £120-250
- ZWB 7-25 Repair: £120-350
Source
Worcester Bosch b1 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 537i manual (PDF)
- Worcester Bosch Bosch Greenstar ZWBR 7-25A manual (PDF)
- Worcester Bosch Greenstar 28 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026