There are two ways a boiler can detect how to adjust flame height, one is using the eBUS the other is the return water temperature, flow etc.
The wall thermostat has two possible functions, one is to control the temperature of the house, the other is to switch off the boiler when not required. Not quite the same.
So with a standard house the boiler supplies hot water to radiators with TRV fitted, and the valves control the room temperatures, however once all rooms are warm, the boiler would start to cycle, so a wall thermostat is placed in the coolest room with no alternative heating or outside door. The thermostats job is to turn off the boiler when all rooms are warm. And the setting needs to be slightly higher than the TRV's and it needs to have no anti-hysteresis software built in.
Alternative where there is air exchanged between rooms as with an open plan house, then some TRV's may be fitted to stop bedrooms over heating, but the main rooms are controlled by a wall thermostat, in this case the thermostat does need to have anti-hysteresis software and likely programmable, the best way to stop the hysteresis is to use a thermostat connected to the eBUS with something like opentherm, this means until the boiler can't turn down the flame height any more, the boiler regulates its output to give the house how much heat it requires, this method means the boiler runs in a more efficient mode. Basic idea is the cooler the return water the more heat extracted from the gas being burnt.
So either the thermostat is simple on/off, or the thermostat is programmable and turns the flame height up and down, there are exceptions where the central heating is hot air rather than circulated water then you may need a simple on/off thermostat which is programmable, but that is rare in the UK, the Hive thermostat is really designed for USA or very old boilers which don't modulate.
The problem is opentherm has not been adopted by all manufacturers, so Bosch for example market their own modulating thermostat, the ideal is likely EvoHome where the eTRV tell the "Thermostat" what is required and the "Thermostat" controls the boiler, using opentherm, although called a thermostat it is really a hub which collects info and decides how much heat is required, it does not directly measure the temperature. There are cheaper versions, Nest will run either as stand alone or can be set to follow, or the valves can be set to follow Nest using IFTTT however it is not as flexible if you want rooms at different temperatures. Nest also uses Opentherm.
Of course one can lash together other systems which will give a little better control to a simple thermostat, you can use eTRV which are self contained which are a lot cheaper than the wifi type, and still have the option to be programmed, however a TRV can be wide open but unless the boiler is running the radiator will be cold, so you want a wall thermostat which does not switch off the boiler, but simply turns it down, then the cheap eTRV can work, the whole idea of a thermostat which simply turns boiler on/off went out years ago, at least when used to control room temperature.
Yes I still use one, as my boiler is Bosch and will not work with OpenTherm. And the Bosch thermostat is hard wired and the people who fitted the central heating were a load of cowboys and they ripped out the wiring to the thermostat and fitted a wireless one, so for me to fit a proper thermostat is a lot of work due to needing to hard wire. Best option for me is likely EvoHome but would still need to set it to switch boiler on/off as boiler not able to work with OpenTherm as said it is Bosch. So since EvoHome is so expensive and it can't be set up proper with my boiler I just have a couple of internet connected eTRV so can program main rooms and set temperatures with phone, thermostat still the wireless one fitted by cowboys, but it works near enough for me.
I just wish some one had told me how the modern systems work before the cowboy firm refitted the central heating, I did get them to correct some errors, like having a power shower on a combi boiler which is illegal, but at the time I thought Bosch Worcester was a good boiler. Well likely it is, but it lacks the ability to work with any other thermostat other than the Bosch Worcester so using the phone is limited to the eTRV.
However been rather disappointed with phone control, idea is it is all automatic, as the phone is within so many miles from home it turns up the temperature, well it does work, but house takes too long to warm up, so only time it could be used is when I go on holiday, and for those few times, I may as well manually alter the temperature, OK using the phone, but manually seems to be defeating the whole idea.
