All now working 100%. After much faffing about ending up total rewire of junction box and setting the NEST to the correct boiler type. See above edits.
Hi Muggles, thanks for your reply. I presently get no hot water when the over ride is pressed. I have seen a reply in a NEST forum on the subject of no HW icon, this might be the problem. When home, I will go back into: settings>equipment>continue>pro setup>continue
to see exactly what boiler is...
I note Jackthom's reply regarding different cylinder stats, however, I have found that most cylinder stats are internally wired as above. I have tried swapping the 1 & 2 about but I still get no hot water. I thought I was supposed to get a hot water icon on the NEST gen 3 Learning room stat but...