As said not enough info, there are in general three ways to control a boiler, low voltage (230 Vac) on/off, extra low voltage (normally 24 volt) on/off, and last is connection the the ebus.
The boiler needs to have cool return water to work efficiently, there are two basic methods, one is the control the boiler from the ebus, Opentherm likely, the other is by using thermostatic radiator valves (TRV) and the lock shield valve, however the latter has a problem, it can never turn completely off, so we use a wall on/off thermostat carefully set to turn off boiler on warm days, but it is not designed to control room temperature, that is the job of the TRV.
Old boilers and oil boilers don't condensate or modulate so they can have a wall thermostat to control room temperature, but modern gas boilers need cool return water around 40°C where with old boilers it could be 60°C and the what the boiler does is measure the return water temperature and control the outgoing water temperature to ensure return says at around 40°C, however if you turn off the boiler externally when it turns back on at full output, and it takes time for the boiler to modulate to correct level to get return water at 40°C, so turning it on/off too often defeats this system.
So the question is do you need a wall thermostat, or can this be manually controlled? I find in the spring as it starts to get warmer, I need to turn down the temperature of the wall thermostat to stop the boiler firing up in the morning and heating the house which will then latter over heat when the sun comes out, so even with a wall thermostat I still use manual control.
The question is how much to spend on control, easy to spend £1000, but an electronic TRV head which is programmable starts at around £10 each, so 10 radiators £100, but for the electronic head to link to the wall thermostat the TRV head price jumps to around £45 to £65 each, plus the cost of hubs and wall thermostats.
So stage one is to consider your goal, even if your going to do it in stages, the first job is the decide what your going to end up with, so you only buy things once.
I got it wrong, I decided I would end up with a Nest wall thermostat linked to Energenie MiHome electronic TRV heads, I bought the heads first which worked very well, in fact that well I did not bother getting the wall thermostat, then when I moved house I put the cheap TRV heads back, and fitted them to this house, there was no way in this house to turn boiler on/off without going outside and down a set of steps, so decided to fit Nest wall thermostat, only to find in the mean time Nest support for Energenie has been removed. But I have oil which does not modulate so no real problem, I just set the wall thermostat and TRV with the same schedule.
But step one find if your boiler can be controlled by the ebus, as no point going through how to set it up if your boiler has not got the option.
