The combustion fan is essential to safe boiler operation. Before ignition can begin, the fan must run to purge the heat exchanger of any residual gas from a previous cycle. If the fan does not reach the correct speed, the boiler will not attempt ignition.
Fault Codes C6 and CE
C6 and CE are the primary fan fault codes on the Worcester Bosch Greenstar range.
C6 indicates that the fan speed is outside the expected range — either too slow (worn motor or capacitor failure) or not running at all (motor failure or wiring fault).
CE typically indicates a fault with the air pressure switch circuit — the pressure switch that confirms to the PCB that the fan is running and generating the correct air pressure in the flue.
Distinguishing C6 from CE:
- C6 = fan speed not confirmed (likely fan motor or capacitor)
- CE = air pressure switch not confirming airflow (likely fan or pressure switch)
Diagnosing Fan Failure
When a Greenstar presents with C6 or CE:
- Check whether the fan attempts to run (you should hear the motor starting up during the ignition sequence)
- If fan runs but fault persists: check air pressure switch and the flexible tube connecting the fan to the switch
- If fan doesn’t run at all: check for 230V supply to the fan motor, then test the motor resistance
- If motor resistance is open circuit: motor has failed
- If motor resistance is normal: check capacitor (run capacitor failure is a common cause of no-start)
Fan Assembly for Greenstar Models
Worcester Bosch fan motors are specific to the boiler series. The CDi Compact, CDi Classic, Si, and Highflow models use different fan assemblies. Always confirm the model number before ordering.
Fan assemblies are complete units — motor, fan wheel, volute casing, and mounting plate.
Installation Notes
Fan motor replacement must be carried out by a Gas Safe registered engineer. After replacement:
- Confirm the fan runs at the correct speed during the pre-ignition purge
- Check that the air pressure switch responds correctly
- Carry out a full combustion check
- Check flue integrity and flue connections at the fan outlet
Need a Recommended Installer?
- HGB Heating Kent — Gas Safe engineers, Kent and Medway
- Boiler Sense — Certified boiler specialists, Kent and South East London