Many thanks for your reply.
isn't there a bypass built into the piping?
Yes there is but this does not affect that the valve is permanently energised. With the boiler being 40kw it needs a bigger heat sink than going around a bypass loop so the residual heat needs to go into a heat sink somewhere which is why Ideal have given the recommended control wiring diagram.
the easiest way is to take the zone valve off the hot water and turn the cylinder stat up,
I am not sure I quite understand this, won't it mean I have no control of hot water temp and what would the thermostat be doing. Without the zone valve it will have nothing to control anyway and water will end up same temp as boiler which is too hot for the shower valves. I face this problem anyway as too hot, hot water is the sympton of failure of the hot water zone valve.
or pipe one of the zones together with the hot water into a diverter so one port will always be open.
This idea looks like it might work I need to think this one through wrt to my control configuration. I am hoping to solve this through wiring rather than plumbing. When I installed the control system I brought all of the control cables (valves, thermostats etc) into one central connection box this makes it easier to toubleshoot the system from one central point just by using a multimeter. It also gives me the flexibility to change and add to this system within this central point.
As a heating system what I have works and controls very well apart from when the boiler finally shuts down and the pump stops, the zone valve remains open. Ideally what should happen is that when the pump stops running at the end of overrun the zone valve is de-energised. I think this is a weakness in the design of the recommended control system but I can't get Ideal to comment on this.
Thanks again