Not Working* SALUS RT500BC

[MarkAqua]

Evening,

I went to commission a boiler this afternoon that I finished fitting saturday.

Baxi Duo-tec 28
Salus RT500BC stat and receiver (the one that plugs into the front of a baxi with their wiring)
Turned on,pressed the sync button on the receiver, nothing.
for some reason no matter what i do it will not pair to the stat I have reset both units, changed jumpers and it jus wont pair, the LED flashes on the receiver.

I've fitted loads of these on baxi before, never had an issue previously

Anyone Help?

regards