For the benefit of any one reading this thread in order to solve wiring problems with Y-Plan please note there are some excellent diagrams here: //www.diynot.com/forums/viewtopic.php?t=8369
Yes you were correct. It was my fault, I had not wired up the HWS line from the thermostat. As I was using a second room stat (not a tank stat as per standard Y Plan drawing) I just copied the connections as I had done them before for the main "room" thermostat.
Sorry for being a numpty and...
Came across this old thread while trying to find a solution to my problem. Posting the following to help others who find this thread.
I have just had a 3 port valve installed to convert my system to Y Plan. The new zone thus created is for the kitchen radiator ( in place of HW tank as shown...