This part is based around the diverter valve section. The diverter valve is a part that only appears in combi boilers. It allows the hot water to be guided to the central heating (radiators, etc.) or to the hot water system (taps, etc.). This feature is what separates a normal boiler from a combi boiler due to the diverter valve allowing use of hot water and heating without the need for a cylinder.
We recommend that all parts are fitted by a fully qualified gas safe certified plumber.