BoilerFaultCodesWorcester Bosch C1 Fault Code
The Worcester Bosch C1 fault code means: your boiler has stopped heating because the internal mechanism that pushes air through the system is not spinning fast enough to allow for safe combustion.. It appears on 26 Worcester Bosch models in our database.
Technical description: Fan speed too low.
What causes the Worcester Bosch C1 fault?
This fault occurs when the boiler's control system detects that the internal fan isn't rotating fast enough to safely expel exhaust gases. It is usually caused by a build-up of dust on the fan blades, a failing motor, or a communication issue from the main control board. If the fan cannot reach the required speed, the boiler will shut down as a safety precaution to prevent fumes from staying inside the unit.
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 C1 fault code
Click a model for the full fault code list and model-specific repair notes.
- 28 Cdi RSF Repair: £250-£450
- 533 Compact
- 535 Compact
- 537i Repair: £180-350
- Bosch Greenstar ZWBR 7-25A
- CDi Repair: £250-£450
- Greenstar 2000 Repair: £180-350
- Greenstar 25 Si Compact Repair: £180-£450
- Greenstar 25HE Repair: £250-£450
- Greenstar 25i (ZWB 7-25) Repair: £180-350
- Greenstar 25Si Compact ErP Repair: £180-£450
- Greenstar 28CDi Compact ErP Repair: £180-350
- Greenstar 30 Si Compact Repair: £180-£450
- Greenstar 30HE Repair: £200-£450
- Greenstar 30Si Compact ErP Repair: £180-£450
- Greenstar CDi Compact Repair: £180-350
- Greenstar Highflow Repair: £200-£450
- Greenstar R 28 HE System Repair: £200-£450
- Greenstar R29 40 HE Repair: £200-450
- Greenstar System Repair: £180-350
- Greenstar ZWB7 Repair: £150-350
- Highflow 400 Electronic BF
- R30 HE Plus Repair: £200-£450
- Worcester 25/30 HE Repair: £220-£450
- ZB 7 27 HE Repair: £180-350
- ZWB 7-25 Repair: £200-400
Source
Worcester Bosch C1 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 CDi manual (PDF)
- Worcester Bosch 535 Compact manual (PDF)
- Worcester Bosch 537i manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026