Post a couple of pictures of your set up, boiler, cylinder, wiring etc.
Would be good to see, there may be a reason behind not using the 4 pipe but without seeing the system it's hard to say
Update2#. My fitter has called and agrees re the four pipe and intends to fit a H1? Control box which will get me round this and go to four pipe? I have also had an update from a seperate engineer about Tado and KM Bus settings. Heres hoping.
Ok So if you recall my fitter fitted a two pipe system to my Viessmann 200w System boiler which was a no-no. This has now been refitted to a four pipe system. Two weeks on and we seem to be heading in the right direction. However I am getting some vibration, later in the day which can be heard in the room below. The engineer advised that I need two bypass valves as the system is presently responding to the standard valves closing and taking longer to switch off without these. This seems to make sense, any thoughts as to this approach?