As you point out it needs to be simple and a standard system so anyone can use and repair. That's why I said sonoff, although never used it, reports are it is simple on/off switching using internet.
I used Energenie simply because when I bought it I thought it would work with Nest, and my son had sung the praises of Nest, and yes Nest is good, but Energenie needs it's own hub, and is a bit expensive.
However any on/off switch would do the same in most cases, so I would guess you have set times and days when rooms are used, and this was the main reason why we went to Energenie we had an alarm which wanted switching off when carers were due, but also switching on after they left, so I had three slots, which I could select which day of week active, I really needed four slots, but also could use IFTTT to get extra slot, and the remote controls mean could work when down stairs and I was upstairs. But using this example may show the limitations, it only had three slots, or times, it could only have three remote controls and also internet.
In comparison with Nest Gen 3 I can set a temperature change every hour, and I do, so in the morning it goes up 0.5°C per hour so the TRV's have time to adjust temperature of each room. I clearly don't know what the premises are used for, but maybe some days heating needs to auto switch on at 5 pm and others 6 pm and others 7 pm and what every is selected needs to have enough slots. I did not find how many slots either Nest or Energenie had until after I had bought them.
Oddly with the Energenie TRV heads I do not seem to have run out of slots, same with Nest, I don't know if there is a limit, other than it needs with Nest an hour between each slot, but TRV heads as far as I am aware I could set to run for 5 minutes if I wanted.
What I would consider, can a motorised valve be swapped for a TRV head or similar? Never looked at it, as had no reason to do it, but a TRV is in essence the same as a motorised valve once an electronic head is fitted, and as far as I can see the controls used for under floor heating and nearly the same as TRV bases, so instead of the zones using zone valves if they used TRV heads either on radiators or on whole system it could mean you can control area temperatures far easier and simpler?
I would look at Drayton Wiser, not used it, but it seems the TRV heads can be linked together where one room has many radiators, my cheap bluetooth TRV heads can be linked but there is a limit of 5 heads which can be linked.
Not sure this is best section to be asking for help in, you need people who have used the systems, may be better in plumbing section?
With oil fired central heating everything is easy, it simply switches on/off, but if gas fired, often the boiler will modulate, i.e. turn down output rather than switch off/on, if gas often zone valves can mess up the system as it wants something that gradually turns up/down not simply on/off.
But how much control do you want? Do you need it on times, or just internet control, when the camera club used a church for meetings what it needed was a remote off, when we arrive we had to arrange chairs so small group always arrived early and we would turn on heating, where the problem lay was on leaving often not turned off. Again back to my alarms having a timed on/off three times a day meant what ever state left in, on the times it would return to schedule. So a timed on at 10:45 pm and off at 11 pm would mean they can turn on when arriving but your sure it is switched off again at 11 pm.
