Hi, Do I need any of this if I am using Valliant ecotec pro combi boiler with VR33 OpenTherm and Nest ?I was able to get the Opentherm, Nest and DHW priority to work once I also installed the VR66, which effectively eliminated the S plan system. The wiring in logic is exactly as you say above Plum47.
I have written about all the steps here in a clean thread (I can't link, you have to search for it)
Vaillant Ecotec system boiler with VR66 and Opentherm (Nest)