No TRV's fitted in lounge where room stat is - you shouldn't anyway, should you?
That is debatable. There are two types of thermostat, those to stop boiler cycling, and those which control room temperature, with a modulating boiler to control room temperature you need a modulating thermostat which connects to the boiler ebus, OpenTherm is a good example, as every time the boiler is turned off by external controls, all heat in the boiler goes out of the flue, and when turns back on again it does so at full output, with my boiler it takes around 20 minutes from turning on to getting warm water back, so to allow the boiler to modulate with an on/off control it needs to run for at least an hour before turning off again, or when it turns off it is still at high output so more heat lost when it turns off.
The books say on/off thermostat is put in a room normally kept cool, on ground floor, with no alternative heating or outside doors, non of my homes have had such a room, so some compromise is required. The idea of the on/off thermostat is to stop boiler cycling, the TRV can control each room, but unless wifi connected to a controller (wall thermostat) it can't tell the boiler when to switch on.
So with a home with no wall thermostat, as the home warms up first the boiler modulates, (turns down) then it starts to cycle off/on, but since boiler doing the control it turns on at a low output, and the off time is slowly increased (anti cycle software) but it can never turn off, as nothing to turn it back on again.
If we fit the on/off thermostat in the hall, every time the front door is opened the hall will cool, if we open the lock shield valve to compensate, then hall heats up too fast, so rest of house gets cold, so we combine the lock shield, TRV and wall thermostat, the TRV is set to start to close around 2°C before the wall thermostat setting, which is low anyway so on a warm day the central heating does not run, so the scenario is:-
Front door opened, hall cools, TRV opens up wide, the radiator starts to reheat room and then the TRV starts to close so heating rate is reduced before the wall thermostat is triggered, in fact the wall thermostat only turns off on warmer days, the boiler simply modulates on cooler days.
So basic thing is you don't fit an on/off thermostat in the room kept warm, as when summer arrives the room will heat up in the morning, then when sun comes out over heat due to sun, so the on/off thermostat is fitted in a cooler room, so when summer arrives it will not turn heating on when likely to be a warm day.
However with the smart thermostat it can be connected to the internet and use the weather reports to decide when not to turn on, so can't say never fit in main room. What is needed is to assess each home on its own merits, things like bay windows and conservatories can mean the sun can cause a massive temperature raise, and there is of course the human machine interface method of control, or the off switch.
But like you I read all the books which said do not fit a TRV in same room as main wall thermostat, likely written before the modulating boiler was invented, but when I did fit a TRV it transformed the heating. Having done it and it worked, I can say in some cases having a TRV and wall on/off thermostat in the same room works. What I can't say is if it would work for you.
