@marpi82 It is a bummer but this is only possible in standalone mode where you can mirror the port that is connected to Central heating boiler controller to an empty port in the switch/router (depending where is it connected) and capture data connecting yourself to the switch port that you choose as destination, then fire up wire shark and you are done, set a capture filter on mac or ip. done

Unfortunately for some reason this supposedly business controller does ot have this basic feature. 

@marpi82 Now that said you will probably find that communication is done using TLS and cannot be decrypted without a man in the middle proxy..if the manufacturer is incomptent they may be using plain text, in which case please alert other people here so they do not buy such an ill-designed stuff.