Drayton Digistat SCR not firing boiler?

Help,
My drayton digistat scr is not firing up the Worcester/bosch 24i junior boiler.
The scr is communicating fine with the Digistat 3 rf however the boiler will not come on. I have tried power cycling the scr and also tried the override button, but nothing works.

I'm sure it is not the bolier at fault as I can put it into test mode and this fires up the boiler and heats the radiators, also I still have hot water.

Any suggestions would be greatly appreciated.