Hi Homealone,
That would be great if you could, i am having difficulty understanding your instructions for the Red/White and red/black wires.
On my boiler, the double black plug goes into the bottom terminal (the "on" postion) on the Power switch, not the Timed/Summer/Const switch which you indicate.
It looks like the following:-
Power
0 (Off) - Blue Cable
Middle position - Brown Cable
1 (On) - Double Black
One Double black cable goes to the Timed/Summer/ Const Switch at position 0 (Timed) and the other goes off to the terminal strip.
I have included a diagram to make things a bit easier to see, perhaps it will help - feel free to butcher it
EDIT: By the way - wat do you mean by "the diagram on the little instruction leaflet" - what instruction leaflet do you mean?