Plenty of options available but depends on what you're calling smart.
You have hit the nail on the head.
so I can control heating from away from home.
I assume looking at Geo-fencing, I seem to remember Tado is quite good, but no experience. Tried Nest, load of rubbish, it will turn the heating off when you leave, but one is nearly home again before it turns it back on. Energenie and Drayton Wiser use IFTTT, did try using it to get another control time, but not really got into it. Telemetry is rather old technology, read about Discworld and the clacks, the French and the English used it in some form, Alexander Bain in 1843 invented the fax machine, but the French got it to work, think there is still one of the pair in Paris, 10 foot tall and weighs 5 ton.
But in the main we consider smart heating as when the TRV can work out how long it takes to reheat a room, and heats the room that much before the set time, so you set the time you want to use the room, and it seems Drayton Wiser TRV claims to do this.
The Geo-fencing is not going to work with most systems, as we don't live 2 hours from home, but the big problem with so much central heating is the boilers are too big. Theory is great, arrive home 6:30 pm, ½ hour to cook the meal, 1 hour to eat the meal, then watch TV, so kitchen heating goes on at 6 pm, dinning room 6:15 pm, and living room 6:45 pm, and finally bedrooms at 10 pm.
But the kitchen radiator can't sink the 6 kW minium output of the boiler, so all the times are up the creak, as the boiler is not running when the dinning room TRV opens.
And the geo-fencing can't start a sequence of events, we can only use fixed times. There are some thermostats which are very poor, as the whole idea is to control each room independently, so Nest which will not connect to TRV heads in a meaning full way, is rubbish.
But the same question has been raised many times, I know Drayton Wiser works, because I have that fitted, and I know Nest is rubbish as I also have that fitted, but then it stops.
The central heating control can be split into sections, the TRV and wall thermostat, and the hub, and some systems the wall thermostat and hub are in the same unit, so wiring can become a problem, with Wiser the hub and the thermostat are separate so you can decide if the TRV will control the room or a wall thermostat, it gives one some flexibility.
EPH does not work with TRV heads, but with motorised valves, Wiser can also control three motorised valves, but to use OpenTherm you need the master/slaves method used by EPH, but EPH does not control TRV heads, and why would you want it to? The TRV is its self a motorised valve.
The way Nest has dropped support for Gen 2, would not be keen on Nest, even if it did connect to TRV heads, Hive has improved with OpenTherm, but early days the connection to TRV stopped if thermostat over 22°C not sure if that now corrected.
