* Boiler spare parts must be fitted by a certified Gas Safe engineer * Orders received before 4pm are usually dispatched for next business day delivery Potterton 5116017 Hydraulic Inlet Assembly 10L/Min in Gold. The Potterton diverter valve is a mechanism that only appears in combi boilers. It allows the hot water to be redirected to the central heating (radiators, etc.) or to the domestic hot water system (taps, etc.). This feature is what makes a combi boiler so popular due to the boiler's being able to provide heating and hot water without requiring a cylinder.