As an electrician I can't ever remember being called back to a faulty thermostat, I have corrected plumbers messes, but as tradesmen unless working in house we often don't get much feed back as to how what we installed worked.
As a house owner very different, if it fails I need to correct it, also if it does not work well. But we all tend to relate to our own home, my first was hot air, expensive to run, but did not matter where the thermostat was as air circulated around the house, so vents open or closed all rooms tended to be same temperature.
Second was open plan, did fit TRV heads to upper floors as they tended to get too hot, but it worked, so did not really think about it, changed from programmer and thermostat to programmable thermostat, but it worked.
Returning to parents house it was in comparison a nightmare, hall cooled quickly when front door opened, living room overheated if sun came out, mainly due to bay windows, upstairs over heated, the best room converted to bedroom was too cold. Originally coal fires, then coke, then gas, then central heating. The main problem was wanted individual room control. Also for living room fast control, when the sun comes out the radiator needed to turn off as quick as possible.
So want radiator only as hot as required, so it cools down faster, this is helped with a modulating boiler, but only if it modulates of course. Turning the boiler off/on does not help, it means the TRV has to work harder adjusting to fast changing water temperature, continuous flow and lower temperatures mean the TRV has a far better chance to adjust to room temperature, and also less likely to over shoot.
So where does the wall thermostat fit into all this? Well the old idea of a wall thermostat in a room with no doors to outside, no alternative heating, and keep cooler than other rooms clearly works with a modulating thermostat, and no TRV in that room, but how many houses have such a room? And also how many houses have modulating thermostats? Using EPH thermostats you can set as master/slave and still use Opentherm modulating control with a zoned home, but that means in the main a door on stairs and upper and lower floors separated, and we only use upper at night, one rarely have doors on the stairs, and two upper floors tend to be used during the day, so only real way is either all TRV control and a simple on/off thermostat to switch off heating in the summer all it does is stop the boiler cycling on warm days, or link at least some TRV's to the main thermostat.
So now the big question, with a boiler able to use a modulating thermostat does the modulating thermostat really work that much better than using the TRV and return water temperature to control the boilers modulation?
The idea of Hive seems good, fit a thermostat in a room, but also link at least some TRV's, which can send a demand for heat, so in essence the wall thermostat is a hub collecting information about the other rooms, it could be without any temperature setting, the EvoHome again uses same idea, although EvoHome can have an OpenTherm module fitted, also Drayton Wiser, where they fall over is where zone valves have been fitted, the Drayton Wiser for example can only work OpenTherm when a single channel model, the two and three channel versions will not work with OpenTherm.
Bosch boilers will not work with OpenTherm and you have to use their own modulating thermostat that does not connect to TRV's.
Even the TRV's don't work as well as expected, the anti-hysteresis software is often too much, I used Energenie and it would take 4 hours to settle at a new temperature, so I cheated and set 2 degrees high for an hour then back down to wanted temperature, the Drayton Wiser claim to work out what is required and work faster, but for any TRV to work water needs to be flowing and at least warm, even if not stinking hot, and any on/off control messes this up.
I did get mother house working well, but moved the same TRV heads to this house with non modulating boiler and no where near as good. In fact the cheaper eQ-3 seem to work better.
But if your eyes have not glazed over yet, it does seem the most important control is the TRV, the wall thermostat is really only a way to collect info from the TRV. Which is why in the main the Nest wall thermostat is rubbish, it does not connect to TRV's, great for first house with hot air system, oh and how are USA houses heated? Clearly designed for USA not the UK.
Most can be made to work, but to get a good system costs an arm and a leg, so we use a compromise. As to geofencing, it depends on time to warm up the house, or more to point rooms, if you have 9 kW of radiator output in the main room you can heat the room fast, and arranging a sequence which rooms first the initial rooms used when returning home can be heated fast, but a 2 kW heater in a large room may maintain the room temperature, but to raise it by 10 degrees takes time, and unless you work an hour from home there is not the time to reheat the home. So simple time works in the main better.
