The basic problem is that the HW will switch on when required. ( I can see the actuator move to the required position on the 3 way valse) However, when I switch on the CH nothing happens and the actuator does not move at all.
I assumed the Synchronous motor was faulty, so replaced it with another unit from Screwfix. However the fault still remains.
I can make the heating come on by manually pulling the lever over to the CH position and it then fires up. The CH stays on and seems to work fine, and the room thermostat switches it on and off at the desired temperature.
The problem happens when the HW switches on and the valve moves over to HW. Afther the HW has swicthed off the valve does not return to the CH position.