The BDR is a relay. The clues are in the names.
Vaillant ecotec plus 835 & evohome & opentherm compatible?
Wireless Receiver for OpenTherm® appliances.
Which will have a relay contact or ( most unlikely ) a solid state switch to complete a circuit when there is a need for the boiler to do something.
EDIT or maybe they have a serial data link to a data port on the boiler to provide for more control functions than just the simple boiler on / boiler off that a single relay contact can provide. That would seem a bit over the top for a domestic heating system.
Looks like you might have added the BDR as an after thought.
And I immediately stated it was a relay.
The clues are in the names.
No point trying back track now though.
The clues are in the names.
No point trying back track now though.