EPH do a hard wired system using zone valves, the wall thermostats are set to master/slaves for the OpenTherm but hard wired to zone valves.
The problem is can't have both, and e-bus control, either TRV or zone valves, which makes sense as TRV's are in a way zone valves.
However often you don't need all TRV heads reporting back to the wall thermostat, in any building some rooms will tend to be the cool rooms, other tend to stay warm, so with a home with 8 rooms, may be 3 rooms need linked TRV heads, and 5 rooms simple programmable heads.
The big question, which no one seems to be able to answer, is how much better is e-bus control over using the return water? Using the return water you can fit wall thermostats in parallel, did this in mothers house, wind direction and sun changed which side of house was cool and which was warm, so fitted a pair of wall thermostats, one each side of house, the TRV stops any room over heating, the wall thermostats stop the boiler cycling when the TRV's are satisfied.
Consider a home without a wall thermostat, only TRV's. Heart of winter no problem, the TRV's will control boiler output by altering the temperature of the return water, and keep each room spot on, however as summer approaches all TRV's will be closed, and the by-pass valve will open, and the boiler will cycle on/off to keep the water in the loop between boiler and by-pass warm, the wall thermostat needs to turn off the boiler when this is likely to happen. But a boiler running between the two limits of maximum and minimum output, will ensure the TRV's can do their job, so the radiators are only just warm enough, this in turn means, if the sun comes out and heats the room, less energy stored in radiator so it stops heating quicker.
There is another option, in the main installation cost means not an option, but fan assisted radiators are far faster at heating a room, and can also cool rooms, but the water is continually circulated, so really need to be in series rather than parallel if you want to allow boiler to modulate. An odd one is OK in the kitchen for example, they are smaller, can even be fitted in the kick space under a cupboard.
I tried geofencing, but the TRV heads let me down, the anti hysteresis software in the TRV head was OTT, using energenie mihome, and set from 16°C to 20°C at 7 am, the room was not at 20°C until 10 am, so set to 22°C at 7 am and 20°C at 8 am it worked A1, at 8 am at 20°C and it would then hold the temperature. But this will not work with geofencing, Drayton Wiser claim their TRV heads work this out, and use algorithms to speed up the reheat.
But TRV heads which link to a hub/thermostat cost £45 - £75, where as I got some bluetooth TRV heads for £15 each (eQ-3) also Terrier i30 are stand alone, so to keep down costs only some heads are wireless connected to a hub/thermostat, most are stand alone.
Seems daft the expensive mihome does not have open window detect, and can't be manually set between comfort and eco, but the cheap eQ-3 can, walk into a room earlier than intended, i.e. go to bedroom early, and press one button to swap eco to comfort setting with cheap TRV head, do same with expensive one, and no controls on the head, you need to fiddle around with phone or PC.
I tend to put mobile phone on charge when I get home, can still answer calls on my watch, but it means I don't have a phone handy to alter the TRV setting. I suppose it is my fault, I could program the google mini to alter the TRV setting with a voice command, however the google mini and Alexa both some times behave like mischief little boys, and do the wrong thing, turning off a light OK you see it got it wrong, set heating wrong, and by time you realise, it is too late.
I had this with geofencing using Nest Gen 3, when you walk past the thermostat it auto detects you and sets to comfort, also if it reports your phone is at home set to comfort, when I go out it detects phone not at home, so sets to eco, with the winds earlier this year the EE mast was damaged local to me, so it detected phone not at home, so set to eco, except when I walked past the thermostat, when it detected me and went to comfort, I had a day and a half before I realised why so cold in the house, then turned off the geofencing option.
And this is the problem, you don't notice straight away, so if a Nest mini turns down heating, likely 3 hours before you think it rather cool, what's going on, then another hour to reheat, so 4 cool hours. So I don't use Nest Mini to set temperature, I do ask it the temperature in the living room etc, but don't allow it to alter temperature.
I do use it to turn on the lights on the stairs, handy when hands full, but not turn bedroom light on/off, I use a remote control for that.
