Wo hoo!
Experts in disagreement is always excellent to behold.
Guys - thanks very much for your help. I will be printing the entire thread and settling myself in for some serious head scratching over the w/end.
Well - an update. I left the system on its boiler-low, pump-medium setting, CH+HW, bypass a fraction open settings and went to work yesterday. Came home last night and the house was cold, boiler pilot light out.
So it must have got unhappy and tripped itself.
Pump was still spinning (sounded quiet = no air? maybe no water??!) so I re-lit the pilot and sparked the boiler onto "low". It complained and re-tripped itself almost straight away.
I switched the pump off upstairs and tried to bleed it - no water came out at first, then only a drop. Re-lit boiler, tripped straight away.
Croydon - did some looking at your post: (Thurs 11:06pm)
The 3 way valve manual lever offers no resistance when the timer is set to CH (it stays down). When its set to HW, the lever offers resistance to being pushed down, makes a winding noise, then slowly pushes the lever back up - at this point if I push it to the right it catches itself in the provided slot.
You are correct - the pump is one floor above the boiler.
Didn't get a chance to try the in-between settings pump trick as the boiler had cacked itself, however I seem to rememver bubbling in the F&E tank when I tried this before.
Anyway - so my next steps are to follow what Croydon and Felix have agreed - CH+HW, open bypass fully, then close bypass fully. Although having said that, the system seems so unhapy now that getting it to go for more than a few seconds may be a challenge.
felix - can you clarify how I would bleed the cylinder coil? Is this where I run HW only with the bypass fully closed?
If I don't blow myself up over the weekend, I'll post some digi pics of the setup if its not solved by then.
Once again , thanks for your help.