BoilerFaultCodesWorcester Bosch A8 Fault Code
The Worcester Bosch A8 fault code means: your boiler's internal components are having trouble communicating with the main control board, preventing the system from starting up.. It appears on 38 Worcester Bosch models in our database.
Technical description: DHW sensor fault: DHW sensor (8000 - 20000 ohms at room temperature), Wiring and connections to sensor.
What causes the Worcester Bosch A8 fault?
This fault occurs when the boiler's main control board loses its digital connection with internal components like the display or the heat engine sensors. It is usually caused by a loose connection in the internal wiring or a physical failure of the electronic circuit board itself, preventing the boiler from sending start-up commands. In some cases, moisture ingress or a power surge may have damaged the sensitive communication pins on the board.
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 A8 fault code
Click a model for the full fault code list and model-specific repair notes.
- 24 RSF Repair: £100-250
- 26 CDi Xtra Repair: £80-220
- 30i Junior Repair: £90-250
- 35 RSF Repair: £90-180
- 537i Repair: £150-250
- CDi Repair: £120-250
- CDi Classic Repair: £90-£250
- CDi Highflow Repair: £150-350
- Danesmoor Repair: £90-220
- Greenstar 12i System Repair: £180-450
- Greenstar 2000 Repair: £150-300
- Greenstar 25 HE Combi Repair: £180-450
- Greenstar 25HE Repair: £150-450
- Greenstar 27CDi Repair: £150-300
- Greenstar 28CDi Repair: £150-300
- Greenstar 30HE Repair: £150-£450
- Greenstar 30si Repair: £120-250
- Greenstar 8000 Repair: £150-300
- Greenstar CDi Compact Repair: £60-220
- Greenstar i Repair: £180-450
- Greenstar R29 40 HE Repair: £150-300
- Greenstar Ri Repair: £180-450
- Greenstar Si Combi / i System Repair: £0-180
- Greenstar System Repair: £150-300
- Heatslave Repair: £90-180
- Hideaway Repair: £90-220
- Highflow 250 Repair: £200-450
- Highflow 300 Repair: £200-450
- Highflow 440 CDi Repair: £200-450
- Highflow 550 CDi Repair: £200-450
- Junior 24i Repair: £90-250
- Junior 28i Repair: £90-180
- R30 HE Plus Repair: £150-350
- Ri 25 HE Repair: £150-300
- Worcester 25/30 HE Repair: £180-450
- WR325 RSF Repair: £180-£450
- ZB 7 27 HE Repair: £150-300
- ZWB 7-25 Repair: £150-350
Source
Worcester Bosch A8 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