I have tried to use eTRV's but since it hard to read meter and actually work out if saving money I can't be 100% as to if it is saving money or not.
The eTRV comes in three flavours, basic stand alone, wifi connected using IFTTT and using a full hub control system like the EvoHome. Mine are the half way types, can use IFTTT but not used at the moment.
The problem is turning the boiler off when not required, the modern boiler has a variable flame height and even the standard TRV has a gradual control so between them in the heart of winter they can keep the home at a very controlled temperature with very little hysteresis. The problem arrives as the weather warms up, the boiler starts to cycle then reaches a point where it needs turning off, and it is how to turn it off which is the problem.
The books say you should select a room and not fit a TRV to that room and set the lock shield valve so that room is last to get warm, however I don't have a room suitable. Heat raises so it needs to be on ground floor, and it should not have any other form of heating, and no doors to outside, that leaves cupboard under stairs, but that has no radiator.
What I have done is break the rules and fit a TRV to hall radiator plus have a wall thermostat in the hall, I set the limit on hall thermostat to 19.5°C then slowly increased the temperature on the TRV until it got the hall after a long time on warm days hot enough to switch off the wall thermostat, it means from cold hall warms up quickly to around 17.5°C then it slows down giving all other rooms time to warm up, no perfect but it does work. Down side is hall has one set temperature, any ideas of cooler in the day and warmer in evening are out, as the two thermostats are careful matched, so can't alter one without the other, it relies on the TRV having around 2°C between starting to close and being fully closed, but wall thermostat is just 0.5°C between on and off.
Once I got that sorted, then I needed to sort the two main down stairs rooms, upstairs seemed to work well with simple TRV's they just give a back ground heat, but back room down stairs gets morning sun and front room evening sun, so both rooms fitted with WiFi TRV heads which have a smaller range between fully open and fully closed to the standard heads around half so 1°C between fully open and fully closed. They control both rooms well, there are two sensors in each head one measures water temperature the other air temperature so it can auto compensate for heat from radiator.
The other thing is you can program them, so 9 pm in back room (living room) it changes from 22°C to 16°C (lowest setting) then at 6 am back to 22°C then at 9 am down to 20°C and at 5 pm up to 22°C. I have found at 6 am the room has still only cooled to 17°C and without having that extra 2°C first thing in the morning it takes ages to hit 20°C so having it set to 22°C in the main it only gets to 20°C in morning.
Although I can alter the temperatures of the two rooms from my phone, it is so slow to both heat and cool it seems rather pointless, so once set it has been left alone. There is a programmer and this is set to switch off heating at 4 am and back on at 6 am this is so the boiler is running when the two rooms call for extra heat. I have a second programmable thermostat in kitchen, I bought it before the eTRV's in a failed attempt to get better control, it is not really used any more, but does allow me to set a boost if required.
Hind sight is easy, and in hind sight the stand alone eTRV's would have done the same job for a 1/3 of the price, the Pegler Terrier i-temp i30 costs around £26.50 where the WiFi Energenie I used cost £75 a pair plus £53 for the hub, however hub also runs smart sockets and my bedroom lights. But £128 v £53 is a lot for something which does the same job. I could expand my system using NEST with will either follow the heads or the heads and follow NEST but that means all rooms at same temperature and the whole idea was independent control, so in real terms either go for cheap option or go whole hog and get something like EvoHome.
As to balancing the system, that will reduce warm up time, but will not do anything once warm as the TRV's control once it is warm. It the lock shield valves are not throttled back then what happens is boiler fires up and easiest radiator to heat gets hot, the return hot water causes the flame height to reduce, once that room is warm the TRV closes and next room is heated and so on, so the boiler never gives out the full amount of heat due to the returning hot water. Until all rooms are warm then the TRV's control the flow and the lock shield valves do nothing.
Before the condensate boiler return water temperature did not matter, only the output temperature was monitored and it was common to attempt to control the whole house with a single wall thermostat, my house still is talked about mothers house above, my house is an open plan designed to be heated with a single gas fire, with central heating the programmable thermostat works well, house before that had hot air central heating all the air is blown around in a circle, vents in each room hot air in and vents in every door for cool air to return to one L shaped living room. I worked well but expensive to run. That house would have also worked well with a programmable thermostat.
As to water temperature needs to be over 60°C to stop legionnaires, and below 80°C to allow condensate to form from flue gases, so I would go mid range. It does not really make that much difference.
You watch after all that I bet you have an old boiler, old boilers only switch on and off, so you don't get the seamless control offered with the new type, or the problems with hot water returning closing down the boiler, but TRV's still work, there needs to be either a special pump with variable speed or a by pass valve, mothers system has two by pass valves one inside the boiler and one outside not a clue why two, will guess plumber did not know there was one inside the boiler. Before the TRV often there was no by pass valve, so before fitting TRV do make sure there is a by pass valve.
At home I do have one odd radiator with a fan built into it, very high output but also very small as radiators go, it has motor speed control and a thermostat both controlling fan for room temperature and stopping fan when water goes cold. It is both fast heating the room, and also allows room to cool fast.
If I wanted to save on the heating bill, likely the heat recovery unit would be high on the list, then I could get rid of all the drafts. But they are expensive.
