I would love to know the answer, however with many boilers access to the terminal block means removing seals, so one has to be gas safe it seems. Yes EvoHome the OpenTherm is an add on, and I have fitted Nest but found the Energenie TRV heads don't follow Nest as they should, the Hive advert seems good, not OpenTherm but the "heat on demand" seems a good way around the problem of working with modulating boilers, but again reports of TRV heads not talking to wall thermostat as it should, and Tado don't want to give out information so that is an unknown.
It no longer worries me as using oil now not gas, but my requests on info in the past have not been very helpful.
I have a "Smart" thermostat, in my case Nest and MiHome Energenie, and it is rare I ever assess it with my phone, well I have used the MiHome Energenie app to turn on the AC in the summer before starting on way home, and I did try GeoFencing with MiHome Energenie but heat up time was too slow, the anti-hysteresis software is too good, heats up to within 2°C of target very fast, but then slows down so it will not over shoot so looking at a couple of hours to reach new temperature.
Nest tells me how long it will burn for to reach the temperature set, but it can be wildly out as it depends if doors left open or closed, and of course temperature set on the MiHome Energenie TRV heads.
So if you take the cheap option, a hard wired programmable wall thermostat off/on type, £35 and programmable stand alone TRV heads £20 each, so looking at with this house £315 with a programmable system for each room, and EvoHome £500 before counting price of TRV heads as each controller only does 12 zones and I have 14 zones, even at 12 zones £700 for TRV heads plus controller at £250 so £950 for the controls. That's three years of oil.
So big question £315 v £950 how much better is it? I brought the MiHome Energenie TRV heads from last house, so have 4 fitted on entrance floor, then 5 bluetooth eQ-3 TRV heads upstairs and in kitchen, the cheap heads seems to work as well as the expensive if not in some ways better, to be frank when I walk into the dinning room I rarely pick up my phone and turn up the temperature, it's too much messing around, however walk into bedroom early, and I will press the comfort/Eco button to lift temperature every time, it's so easy. Also I can see at a glance what temperature they are set at, with the MiHome Energenie TRV head I have to get out my phone or PC.
I got my eQ-3 heads for £15 each, but that outlet has stopped selling them now, the non bluetooth are £10 each on some web sites. Bluetooth makes them easy to set the schedule, it's a bit of a long winded job doing in manually. Worth the extra £5 I think, but they can only be paired with one phone.
I would love some one to tell me "I have XYZ and it works great because ABC." however I have heard some good reports on EvoHome, but also seen people singing praises of Nest, and when you ask how they got the TRV heads to follow, you get answer "Oh I haven't got those." so only half a system, so the report means nothing.
Don't get me wrong MiHome Energenie TRV heads do work, last house we had a problem with the morning sun causing the living room temperature to rocket, it would hit the bay windows and before you realised the room was at 27°C once the TRV heads were fitted and the lock shield valves adjusted this dropped to 24°C with room set to 21°C. Can't stop the sun, but could ensure when sun shines the radiator turns off, in the other rooms it kept rooms to within 0.5°C of setting, so worked very well, when fitted on the return side of radiator the lock shield valve setting was rather critical, they work better on the supply side, but still work either side.
In the old house hall radiator set 0.5°C below the wall thermostat and it only switched off the boiler as weather improved, the boiler modulated with the return water temperature very well. This house being oil, there is no modulation, so TRV's don't work quite as well. But they do work, and the eQ-3 seem to work just as well as the Energenie.
I have tried to be honest, I think EvoHome would have worked better, the reason for Nest was only two wires between main house and flat where the boiler is, and the Nest thermostat can control central heating and hot water plus be powered with just two wires, it was not got because it was smart, however it does seem to work well, very easy to over ride if cold, or turn down when leaving house, I have it set to increase temperature by 1 degree at 5 pm, which means if I turn it down when leaving house in morning it auto turns up again at 5 pm, so always return to warm house. But any programmable thermostat would do the same. However we have a Flomasta in other house, and on Friday when I visited had to read instructions to work out how to manually temporary raise the temperature, so easy with Nest, just turn the dial.
One odd thing MiHome Energenie software on the phone will also work Nest, but not on the PC. So on the phone when I had MiHome Energenie TRV heads set to follow, turned Nest up or down with the MiHome Energenie software and all TRV heads followed as they should do, but alter Nest with the set schedule or with Nest software, and half the time they failed to follow. However use the phone to look at temperature without altering anything, and then TRV heads followed. I am using a Samsung phone, wonder if I used an iPhone if it would work different?
