I think you have posted this in wrong section. In general thermostats have either 2 or 3 wires to them. The battery operated type are normally only two wire and are considered as volt free this means the boiler could be 24 volt or 230 volt control and thermostat would still work. However the older units used a bi-metal strip and the design results in a large difference between switch on and switch off temperature to ensure rapid opening and closing of contacts and to reduce this they also have a heater and a neutral connection and will only work with a 230 volt supply and the feed and return have to be right way around. So I always provided a triple and earth cable to the thermostat in case the latter type was used.
There is also a third type which uses a remote thermocouple which connects to a box of tricks which not only monitors inside but also outside temperature and keeps the house cooler when it is warm outside.
As to what will fit the boiler and system you have you are better posting in heating and ventilating section.
Most combi boilers have connections on the printed circuit board so you can use an external room stat (that is external to the boiler) and usually a twin and earth 1mm squared cable is suffice but check manufacturers handbook first.
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