Siemens 28mm 2 Port Zone Valve CZV228, this Diverter Valve is a part that only appears in combi boilers, it allows the hot water to be sent to the central heating system (radiators, etc.) or to the hot water system (taps, etc.). This feature is what separates a normal boiler from a combination boiler due to the fact that a combi boiler wouldn?t require a cylinder to provide heating and hot water. Weather it?s a Condensing Combi boiler or a non condensing combi the Diverter Valve functions are the same. Combi is short for combination, and you can have a condensing combination boiler or a standard efficiency combination boiler. Siemens 28mm 2 Port Zone Valve CZV228 is also known as the 3 way valve, Hydraulic Outlet Assembly, Change over Valve, 3 Way Diverter, Three Way Diverter Valve, and Motorised Valve. If you have no hot water, or there is no central heating, the diverter valve is leaking, or it?s stuck or gone it?s a faulty valve, and then always refer to the manufacturer?s instructions. Heatingspares247.com is one of the UK?s largest independent Boiler Parts & Heating Spares Stockist, We specialise in the supply of Genuine Boiler Spare Parts from all the leading Manufacturers. Services available are trade counter pick up, Next working day standard delivery, next working day AM delivery and Saturday delivery. We also operate same day express delivery service. Our Opening timers are Monday to Saturday, 8AM to 5.30PM Heatingspares247.com is an Approved Boiler Spare Parts Stockist, and we guarantee to supply Genuine Heating Spares from the Boiler Manufacturers.