This Vaillant Replacement Diverter Valve is suitable for Thermo Compact VC-VCW (balanced flue), COMBI compact VCW (conventional flue) and COMBI compact VCW (fan-assisted) 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 are able to provide both heating and hot water without the need for a storage cylinder.