I would be going back to what you are aiming for.
So let me talk about "Smart"
1) Ability to remotely turn heating on/off.
2) To have the heating turn on/off automatic as you leave or enter area where home is "Goefencing"
3) Have a timed thermostatic control in each room.
These are not really smart, so to work out when it is going to be warm latter in the day so inhibit heating early in the day would be smart. Not seen anything do that.
However measuring outside temperature or connecting to internet reports is done.
So in the main we are looking for using less energy, so central boiler, but each room independently controlled, the problem is where builders have part done the job, using components which don't lend themselves to being expanded on.
EPH do a thermostat which can control a motorised valve hard wired independent to the boiler also hard wired, the latter using OpenTherm so it modulates boiler but switches the motorised valve, and you set the thermostat as master/slave with up to 10 units.
There is in the main not point in mixing types of motorised valve, and an electronic head on a thermostatic radiator valve (TRV) is clearly a motorised valve. There are exceptions like my home where hard wired motorised valves select main house or flat, but within the main house electronic TRV's in each room.
So in many homes to increase control means to remove some of the control already installed. Other than EPH it seems we can't control the modulation with hard wired motorised valves, so upgrading from hard wired motorised valves to wifi controlled motorised valves can allow the move from on/off control to modulated control.
There is some debate over the advantage of gaining the latent heat from flue gases, the boiler may be designed to gain that energy, but the system often switches boiler on/off so messing up the boilers system used to gain latent heat.
So the big question is why do we have on/off wall thermostats if the boiler is controlled by the return water temperature, well the problem is a TRV can't turn the boiler on, so we put a on/off wall thermostat in a room normally kept cool on the ground floor where there are no outside doors and no alternative heating including sun through the window, don't know your home, but in my house no such room. However it is to automatic turn off the heating on a warm day, and turn it on with a cold day, so maybe it should be outside?
The better option is to have a hub of some type, connected to the TRV heads, so the TRV heads tell the boiler when to run, and most the so called "Smart" wall thermostats do just this, they may also measure the temperature in the room, but they also are triggered by the TRV heads.
However this is all well and good with a hydraulic system, but with a hot air system the air is circulated around the house, so often a single wall thermostat is enough, due to air being circulated, so there are some thermostats which don't connect to TRV heads, Nest, Moes etc. This does not stop them from being used with a hydraulic system, but they are not really best suited for the system, Nest it seems in USA have released temperature sensors so it can monitor multi-rooms, but not released in the UK.
The problem with the fancy system is it is not cheap, so we tend to compromise, fit two or three wifi connected TRV heads linked to main wall thermostat, but most TRV's may be electronic so have a program as to when to heat rooms, but not wifi connected, some eQ-3 for example do have bluetooth so don't need to bend down to manually program, but still not connected to wall thermostat.
So what are your aims, once one knows what you are trying to do, then one can point to possible ways to do it.
