As has been said you can't control hot water temperature with Hive .
You could if you so wish use the second channel time hot water on and off. Fairly normal to not have oil combi's on from say 11 to 6.
Your boiler should have a permanent live plus neutral and earth it can possibly be wired a number of different ways.
It may have a stat wired directly or a switched heating and switched hot water supply.
There are also other options!
Only way to tell is to take off boiler wiring cover and have a look.
It all very clearly marked on connectors/ board what they are.