Thanks for this - really helpful! I’ll give it a go and let you know how I get on. Cheers 
I would install the Hive receiver in the cylinder cupboard with some 5 core flex, or 2 x 3 core.
The neutral connected to the terminal with all the blue wires in the connection box, and the live to the terminal with the 3 brown and 3 grey wires in it.
Number 3 on the Hive would connect to the last terminal on the right hand side with the brown flex that is in that terminal.
Number 4 on the Hive would connect to the brown wire of the downstairs zone valve whichever it is.
You would also need to disconnect the black wire which was connected to that zone valve and the brown wire that is in the same cable as the black wire you have just disconnected.
Where the honeywell clock is you would need to join the 2 blue wire with a connector and put a separate connector on each of the 2 brown wires. Then put a 1 gang blank plate on the box.
With this the Hive will control your hot water and downstairs heating and the existing thermostat will control the upstairs.
When you get the multi zone for upstairs come back for info on how to wire it up.
If you want the Hive you have now to operate both zones then just put the brown wire from both zone valves together in the connection to terminal 4 from the Hive.
Then disconnect the black wire that was connected to the upstairs zone valve brown wire and the brown wire in the same cable as the black.
QED
