The diverter valve is a part that only appears in combi boilers. It allows the hot water to be directed to the central heating system (radiators, etc.) or to the hot water system (taps, etc.). This feature is what makes a combi boiler so popular 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.