I have a problem that I would really appreciate help with, I have a Remeha Avanta Plus combi bolier and need to connect a Salus Rt 500RF too it. Any assistance would be greatly appreciated.
As your boiler supports opentherm, an opentherm thermostat would have been a better choice. The stat wires into block X2 after removing the link between 1 and 4.
Look at Honeywell for a reliable opentherm roomstat. I would recommend changing the address on the salus from the factory default to prevent nuisance operation in case any of your neighbours have a salus stat.