Where you have like me in real terms two houses working from the same oil fired boiler (non modulating) then zone valves to select which area is heated granny flat or main house makes sense.
However in the main house, each room has a different use, we give them names, kitchen, living room, dinning room, office, craft room, bedroom 1, and bedroom 2. Does not really matter what name you call the room, but each room has a different heating requirement, by 8 pm the dinning room is finished with, by 7 pm the kitchen is finished with, craft room and office no pre-set times, and of course internal doors not always closed, so through the house two temperatures, we will call it eco temperature and comfort temperature. Eco set around 17°C and any room not in use is allowed to fall to Eco temperature, not too cold so when room is used, it does not take long to heat to comfort temperature of 20.5°C, either using phone, or simply pressing a button swaps from eco to comfort or comfort to eco. In real terms every room is it's own zone. But no zone valve, it is the thermostatic radiator valve (TRV) with programmable head with controls each zone. The programmable heads start at around £10 each so not super expensive.
In my house still use zone valves to select main house or flat, but in my case the boiler is oil fired, and not modulating, last house boiler was gas, and would modulate, so all room temperature control needs to be done with the TRV setting or the boiler will not modulate correctly, so the old idea of a thermostat working a zone valve which in turn works the boiler does not any longer work with gas modulating boilers as it stops the boiler modulating correctly so wastes energy.
There are two ways to control the boiler modulation, one is with return water temperature, the other is connection to boiler ebus, with some thing like Tado or EvoHome using opentherm OK ebus works well, but with many boilers the wall thermostat using ebus is fitted in just one room, all other rooms need to be set to heat faster than the room with thermostat for it to work, and there is a problem using only water as control, as on a warm day, there is nothing to tell boiler to stop, so if left it would cycle on/off all summer.
So we do still fit wall thermostats, but their job has changed, they no longer set the room temperature, they are there to turn off heating when weather has improved.
I have Nest and 9 electronic TRV heads. It suited in my house which is oil heated, however I really do like the idea of Hive, the wall thermostat with Hive is simple off/on, which at first glance seems wrong for modern modulating boiler, however the clever bit is how they link to the Hive TRV heads, so when any head needs heat, it sends a "demand for heat" to the wall thermostat which will then turn on for ½ hour, so while any Hive programmed TRV head needs heat, boiler runs, and its output is controlled by return water, the wall thermostat is simply a relay, using the Hive method yes it could power a zone valve which powers the boiler, but why bother? May just as well use each TRV head to form a zone.
Problem is cost, £60 a head mounts up, with 13 rooms that's a lot of money, however what I have done, although not using Hive, is to use expensive TRV heads in the main rooms, but cheap eQ-3 programmable heads in the rest, the Terrier i30 is another cheap stand alone programmable TRV head.
To my mind the problem is Hive TRV heads only work with Hive or as stand alone, and it is the same with most other makes, so once to select a make of electronic TRV paired head, your stuck with that make, I know very little about wet underfloor heating, I know they use a head very like a TRV head to control it, but I don't know if you can control the UFH with a Hive, EvoHome, Tado or any other make of head. However I know with electric the limit of floor temperature is some thing like 27°C which is too low to heat most rooms to a comfortable 21°C so the floor heating is supplemented with radiators so control is with the radiator not the under floor heating. Clearly with heat recovery units, and leaving the heating on 24/7 then UFH can work well, but we tend to turn off heating when the room is not used, which in turn means the time to heat room from stand-by temperature to working temperature is rather important, the fan assisted radiator is the fastest to heat up room, and smallest, however these also have a problem, as the water flow is not normally controlled, water always flows, but the fan alters speed to maintain room temperature.
As with any system, it can be thrown in, and then you try to make a silk purse from a sows ear, or it can be designed, unfortunately in the main the former method is used, not only central heating, many things in the home are the same, it seems it's been that way for 100's of years, why would anyone fit a coal fire in a room without ducting to bring in combustion air so as not to cause a draft when used? But finding a home where the combustion air was ducted is rare. There are two methods it seems 1) that's the way we have always done it. 2) that's the best method for this house.
First two houses worked, never thought about heating, then went to live with mother, my thoughts were why does this house not work, where the others did? It was nothing to do with central heating boiler or radiators, it was basic house design, other two houses were open plan, mothers house had doors on every room. So if there is a door on a room, then that room needs to be considered as a zone, cost of 13 zone valves and 13 wall thermostats would be silly, so the TRV is king for room control.
