Hi - hope you had a good break! I have ordered the 3-way mixer from Wita ( the manufacturers ) as I already have the original servo which apparently serves both the 3 and 4 way mixers. Once that arrives (from Germany) I will be altering the pipe-work to put the servo-mixer and UFH pump to serve both ground and 1st floor manifolds - which will each then have a 2-port zone valve to open and close as needed. My thinking is that the Delta should be able to be wired as per the drawing? So at the minute everything is still operated manually. I really appreciate all your thoughts and help on this - I now have a much better understanding of the system - even though I still have to resolve the wiring between the Delta and the junction box. Not sure what will go where, so am still trying to get my brain round that. If you have any further ideas, they would be more than welcome.