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 DHW system (taps, etc.). This feature is what seperates a normal boiler from a combi boiler due to the fact that a combi boiler wouldn’t require a cylinder to provide heating and hot water.
We recommend that all parts are fitted by a fully qualified gas safe certified plumber.