This Vaillant Replacement Diverter Valve is compatible with Ecotec VUI (condensing), Ecotec VUW (condensing) and Guernsey/Jersey only (condensing) boilers. A directional water device in combi boilers, a diverter valve directs hot water into a heating system or a hot water system. This feature means that combis can provide both heating and hot water without the need for a storage cylinder. Boiler spare parts must be fitted by a certified Gas Safe engineer. Vaillant 0020010295 15Mm Non Return Valve. Fits Vaillant Ecotec, Unistor, VUI and VUW ranges. Always ensure a qualified engineer maintains your gas appliances.