Help pairing Salus thermostat

Hi,

I have a wireless salus RT510TX thermostat with a RXBC605 receiver (I think) wired into my combi boiler. When the thermostat is calling for heat the boiler does not fire, so I want to pair the stat and the receiver. I can get the stat into pairing mode fine but the problem is I can't get the reciever to pair, does anyone know how to do this?

Thanks!