Your boiler can use two completely different types of thermostat, there is a problem with modulating boilers autumn and spring where they continue to cycle when weather is warm enough, to stop this one can fit a on/off thermostat in the coldest room, with no outside door, and no alternative form of heating to turn boiler off when all rooms are warm. During the winter this thermostat should never turn off, the TRV's control room temperatures and the return water temperature controls the boiler. The thermostat should NOT have anti hysteresis software built in, but you clearly want it to fail safe, so in the main wireless not suitable for this application.
There is a completely different thermostat for controlling main room temperature, this connects to Bus shown under the on/off thermostat connection and instead of turning boiler on/off it adjusts the flame up and down.
Some thermostats have both connections for example Nest.
It seems your boiler has three options, however there is a star on the 230 volt option and I can't read what it says, but for either of the other options you need 5 core cable. The thermostat you have it seems is very basic, so X1 L, N, Earth connect to thermostat L, N, and earth, then X100 RT 24 you remove link and connect to 3 and 4 of thermostat.
With more expensive thermostats if the batteries go flat the thermostat base if no signal every 1/2 hour will auto turn off, i.e. it fails safe, cheap one will just continue doing what they were doing before the batteries went flat, so I walked into my mothers house and the heat hit me, with room at 27°C. However the more expensive types also seem to have anti hysteresis software, what this does is start turning off/on before the heat selected so it does not over shoot, this you don't want, whole idea of on/off thermostat is to reduce cycling of the boiler not to increase it.
Having said this I know I have wrong thermostat, it may not be good for the boiler, but it works, to an extent at least, and I intend to move, so not either hard wiring or fitting Nest, in my case should fit Nest, as it can talk to my eTRV heads, but I am too lazy to fit one.