Sime Diverter Valve
The diverter valve is directional water mechanism that only appears in combi boilers. It allows the hot water to be directed to the heating system (radiators, etc.) or to the DHW system (taps, etc.). This feature is what seperates a normal boiler from a combi boiler due to the fact the boiler can provide hot water and heating without the need for a cylinder.

Sime 6281540 Diaphragm Kit - Friendly Technyl Format/Format System
Part No: 2041798 MPN: 6281540/SIM