Worcester Bosch is the UK’s most popular boiler brand — and with good reason. The Greenstar range has consistently topped industry satisfaction surveys, with a reputation for reliability that earns it a dominant position in the new-install market. But even the best boilers fail. When a Greenstar develops a fault, genuine OEM spare parts are essential to restore it to manufacturer specification.
We stock a comprehensive range of Worcester Bosch Greenstar spares, including PCBs, fan motors, diverter valves, heat exchangers, ignition electrodes, flow sensors, and pressure vessels — for both current models and older Greenstar CDi, Si, and Junior units.
Key Boiler Ranges
Greenstar CDi (Combi)
The CDi range — Classic, Compact, System, and Regular variants — is the current mainstream Worcester Bosch offering. Available in outputs from 24kW to 42kW for combi configurations. The CDi Classic is the most commonly installed combi boiler in the UK.
Key parts for CDi: PCB (87483004610 is a common CDi Compact PCB), fan assembly, diverter valve, flow sensor, ignition lead and electrode, heat exchanger, pump assembly.
Greenstar Si
The Si series has largely replaced the older CDi. Si models feature an updated heat exchanger design and revised PCB architecture. PCBs are not interchangeable between CDi and Si ranges — always confirm model number.
Greenstar Junior
The Greenstar Junior is an older regular (heat-only) boiler, still widely installed in properties with traditional vented cylinder setups.
Greenstar 4000 and 8000
Worcester Bosch’s current premium ranges, introduced from 2019. PCBs for 4000 and 8000 series differ from older Greenstar generations.
Most-Searched Worcester Bosch Parts
PCB (Printed Circuit Board): PCB failure usually presents as persistent lockout, completely dead boiler, or erratic behaviour. Common part numbers: 87483004610 (CDi Compact), 87483002370 (CDi Classic), 8716118413 (24i/28i Junior).
Fan Motor: Fan faults on Worcester Bosch Greenstar are typically indicated by fault codes C6 or CE.
Diverter Valve: A common failure point on Greenstar combis presenting as either no hot water or no heating.
Flow Sensor (NTC Thermistor): Failure causes incorrect modulation and fault codes.
Heat Exchanger: Primary and secondary heat exchangers stocked for all major Greenstar ranges.
Ignition Electrode and Lead: Ignition failure on Worcester Bosch presents as fault code EA. These are wear items — inspect at every annual service.
Worcester Bosch Fault Codes
E9 — Overheating Lockout
The boiler has reached a temperature higher than its safety threshold. Do not reset without investigating the root cause.
Parts to check: Circulation pump, pump capacitor, heat exchanger, high-limit thermostat.
EA — Ignition Lockout
The boiler has attempted ignition three times and failed to establish a flame.
Parts to check: Ignition electrode, ignition lead (HT cable), gas valve, PCB.
C6 / CE — Fan Fault
Fan speed is outside the expected range, or the air pressure switch is not responding correctly.
Parts to check: Fan motor assembly, air pressure switch.
E2 — NTC Sensor Fault
The flow or return temperature sensor is reading outside its expected range. Usually a failed sensor rather than an actual temperature condition.
Parts to check: Flow NTC sensor, return NTC sensor.
D5 / D4 — Low Water Pressure
Not a component fault — indicates system pressure has dropped below the operating threshold. Re-pressurise the system via the filling loop. If pressure drops repeatedly, investigate expansion vessel charge and PRV condition.
Compatible Models Served
Greenstar 24i, 28i, 30i, 35i, 38i, 42i (CDi, Si, System, Regular variants), Greenstar Junior 24i/28i, Greenstar 4000/8000 series, Highflow 400.
Need a Worcester Bosch Engineer Near You?
Genuine parts are only half the equation. For fault diagnosis, PCB replacement, gas valve work, or full boiler service and repair, you need a Gas Safe registered engineer.
Our Recommended Installers have experience across the Worcester Bosch Greenstar range:
- HGB Heating Kent — Gas Safe engineers, Worcester Bosch specialists, Kent and Medway
- Boiler Sense — Certified boiler specialists, Worcester Bosch and all major brands, Kent and South East London
We supply the parts. They do the fitting.