Thank you for your reply
The head only gets very hot after heating is stopped calling and no HW called. Yes the valve was new and has been replace by a plumber and he replaced again as he thought was faulty!
The wiring is the same as link to Honeywell diagram, apart from...
I replaced a 3 way valve (V4073) as rads where getting hot when just HW on, that part is now fine. But after CH switches off, from room stat or from programmer/timer, there is a faint buzz coming from the valve head and after a short time the head becomes very HOT!
(If HW is still...