How to Replace a Worcester Bosch Diverter Cartridge (UK)
Specific guide for Worcester Greenstar diverter cartridge 87186445880. Symptoms, tools, refit torque.
Worcester Bosch
Applies to
Worcester Greenstar 24i/28i/30i/25Si/29CDi/30CDi Junior and Compact ranges built 2011–present. Later 8000 series uses a different assembly.
Symptoms
- No heating, DHW works fine.
- Heating lukewarm, cannot reach setpoint.
- EA338 or D3 diverter fault on display.
Fit
Isolate all three service valves. Drop pressure to zero. Remove the black plastic clip on the diverter body. Pull cartridge straight out. Grease new O-rings with Fernox LSX. Refit and re-pressurise to 1.2 bar.
Frequently asked questions
- Do I need to reset the boiler after fitting?
- No — auto-detected. Simply run through a heating and DHW demand to verify.
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