BoilerFaultCodesWorcester Bosch 9U Fault Code
The Worcester Bosch 9U fault code means: your boiler's internal computer is failing to recognize a vital communication chip, which is preventing the heating system from operating safely.. It appears on 10 Worcester Bosch models in our database.
Technical description: HCM (Heat Control Module) - Problem with the code plug (faulty or not connected)
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 9U fault code
Click a model for the full fault code list and model-specific repair notes.
- 533 Compact
- 535 Compact
- Greenstar 25 Si Compact Repair: £250-450
- Greenstar 25Si Compact ErP Repair: £250-450
- Greenstar 27i System Compact ErP Repair: £250-450
- Greenstar 28CDi 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: £150-250
Source
Worcester Bosch 9U 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