Folks, an update here. Managed to figure it out in the end, with the help of the tado chat support. Apparently, when my thermostat shipped out with some other configuration (Opentherm I assume), instead of relay mode, so the Support person changed that for me OTA, and lo and behold it works now...
Thanks again to @RandomGrinch and @CBW for the help here!!
Thanks again to @RandomGrinch and @CBW for the help here!!