Problem fixed! Was faulty electonics in actuator of motorised valve. Contacted Tower mentioned forums, asked for replacement actuator. One was sent in post - easy job to wire - provided you have a very small flat headed scredriver for wires in your Controller panel - all one block all colour coded.
Note your actuator should have a 3 year warranty, but Tower sent me replacement one without asking for age. No drain down, just had to turnlocal isolator off - any queries feel free to ring me on 07801 71 6368 or 01257 226312. radiators all toasty hot and working independently from hot water
Merry Xmas
Jim
December 2008