There are four areas of interest.
One the boiler.
Two the timer (normally called a programmer)
Three the wiring centre.
Four the thermostat.
Since you want to use a wireless thermostat the base does not need to go to same place as the old thermostat, if replacing a thermostat my first thing is look at the boiler, so find the installation instructions on the internet and do a word search for ebus and opentherm, so if it can use an opentherm or ebus connected likely that is best way forward.
Next look at the system, is it a combination boiler or does it have separate boiler for domestic hot water and central heating, or does the central heating boiler heat a storage tank?
If the latter how many valves and pumps, and are the valves two port or three port, this gives you an idea what plan it is using.
Also why do you want a new thermostat? Some times the old thermostat can work better than the new, if the thermostat switches on/off and the boiler is a condensate type, then the job of the thermostat is in the main to stop it cycling in the summer months, the thermostatic radiator valve (TRV) does all the setting of room temperatures, and although a cheap hard wired thermostat can stop cycling, as you move to wireless there is a massive jump, cheap wireless don't fail save, mid range have anti-hysteresis software which messes up the boiler so expensive to run, so you jump to the higher range which in the main link to the TRV, so you jump from £35 for a programmable hard wired, to £350 plus for thermostat and TRV heads.
The mid range are OK for oil boilers and old gas boilers before they became condensing, but not so good for modern gas, there are exceptions of course, I am talking in general terms.
Anyway start with saying what you want the new thermostat for, to look good, so you can move room to room, so you can have different temperatures at different times of day, there may be a simple method you have not considered.
