Is my Siemens room thermostat wired in correctly?

I have a Siemens RDJ10RF room thermostat set fitted to my Vaillant Ecotech Plus 831 boiler. The remote room stat talks to the receiver but the boiler fails to start/stop on command from the receiver.

My concern is that the receiver is not connected to the boiler correctly, I have opened the casing and and the wiring just doesn't seem right. Despite several searches online I can't find wiring instructions for the Siemens receiver.

Any help and advice appreciated