The Baxi hydraulic venturi assembly part is based around the diverter valve section. The diverter valve is a directional water device that only appears in combi boilers. It allows the hot water to be directed to the heating system (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.

Brand Name	Baxi