I don't like admitting it, however in hind sight I got it wrong. I like you with the Hive went for a half hearted option rather than biting the bullet and going the whole hog. The best option with a water system is to let the eTRV control the rooms and for them to also connect to a hub which in turns controls the boiler, EvoHome is a good example, with hot air systems like used in the USA then because the air circulates in the house a single thermostat will control the whole house at one set temperature, however with the hot water system used in the UK each room can be individually controlled, and the boilers are designed to be controlled by the TRV, they have variable flame height and the return water temperature controls the flame height, so while the TRV is controlling you have a adapting system which has a very low hysteresis.
However there is a problem, when spring arrives the boiler will start cycling as the heating is using less than minimum flame height will allow, so we fit wall thermostats to turn off the system as the days warm up. However the thermostat needs to hand shake with the TRV, there are many ways to get the hand shaking the simple one is to set the wall thermostat either in a room without a TRV or at the same temperature as the TRV, with the latter you can see the problem, although the Hive or Nest thermostat may be settable with a computer or phone, the standard TRV is not, so then you start looking at eTRV's instead.
Every house is different, there is no one size fits all, however in my mothers house I found rooms were slow heating and cooling and although I could set the eTRV to change temperature every half hour, the room will simply not change that quick, set the room at 16°C from evening setting of 20°C over night, and 6 am it has still not fully cooled down before you are wanting it to return to 18°C for the day, unless something like the EvoHome the boiler may not fire up for more than 1/2 an hour which is not enough for house to warm up again, all my big ideas of saving money by only using what I needed simply did not work.
After buying the gear I did not really want to dump it and start again, and after a lot of careful monitoring I have got it to sort of work, but it has a fixed program as to when the rooms heat and cool as although the eTRV is a "If This Then That" ITTT device, the thermostat and programmer is not, and it takes so long to heat and cool all the big ideas of using a phone have gone out of the window.
Learn from my error, either cheap option and simple programmable thermostat, or whole hog and something like EvoHome, the half way option is a waste of money, it's all or nothing.
