BoilerFaultCodesWorcester Bosch d1 Fault Code
Also written as D1 — same fault.
The Worcester Bosch d1 fault code means: your boiler has lost communication with a key internal component that tells it how to regulate your heating and hot water, causing the system to stop working as a precaution.. It appears on 16 Worcester Bosch models in our database.
Technical description: No return signal from LSM (Low Voltage Switch Module).
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 d1 fault code
Click a model for the full fault code list and model-specific repair notes.
- 533 Compact
- 535 Compact
- Greenstar 2000 Repair: £150-250
- Greenstar 25 Si Repair: £150-250
- Greenstar 25 Si Compact Repair: £120-£220
- Greenstar 25i (ZWB 7-25) Repair: £150-300
- Greenstar 25Si Compact ErP Repair: £150-£300
- Greenstar 27i System Compact ErP Repair: £120-£220
- Greenstar 28CDi Compact ErP Repair: £150-£300
- Greenstar 30 Si Compact Repair: £120-£220
- Greenstar 30i System Compact ErP Repair: £120-£220
- Greenstar 30si Repair: £150-250
- Greenstar 30Si Compact ErP Repair: £150-£300
- Greenstar 35 CDi range Repair: £180-450
- Greenstar CDi Compact Repair: £150-250
- Worcester 25/30 HE Repair: £100-£180
Source
Worcester Bosch d1 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 30si manual (PDF)
- Worcester Bosch Greenstar 30 Si Compact manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026