I have to apologise, I am a total newbie and what is quite simple I have managed to confuse everyone.
The problem is that the Valve thing is after the T Piece and not before, we even went into a neighbours house to compare systems (as it is a new deveopment and all built by the same...
A Plumber visited today and after some thoughtfull diagnostic found that the pipe work was wrong.
There is an Automatic Valve that directs water when both the Hot water 2 port valve and the CH 2 port valve are closed. Well this was in the wrong place and was creating a shortcut for the hot...
I have a Potterton Boiler and Santon Cylinder (PP150B Indirect)
I have Central Heating but no Hot Water.
I am confused because I have a silver Honeywell (400 3916 001) box and the pipes on both sides of this are very HOT.
I have a black seimens box (ZA-V222C) seimens is also the boiler...