cosy - (similar style product), only used it for heating as combi boiler so water is on demand.
Fitting - someone did it for us as part of the deal!
3 (or more) boxes:-
1. A box placed with the boiler. This is wired into the boiler somehow and is powered from the boiler. This is a receiver and overrides the normal thermostats call (on off) for heating.
2. Wireless themostat(s) - just need plugging into the mains. No doubt there is some kind of pairing up needed if you add extras.
3. Wireless control box. This needs plugging into the mains and ethernet connecting into the router. This is the bit that receives from the themostat or via internet and tells the boiler what to do.
Sorry can't be more specific. I guess nest/hive are similar and I have no idea how the water/multi zone heating stuff works as we have a very simple system.
Ta, ours is the same sort of thing with a combi boiler on demand water, will have a speak to the sparky and see if he has an idea?