Thank you Mr happy it was the key pad in the Annexe stopping the comms, I disconnecting Data and Clock from it and the others came back to life. When you exit installation mode it flags Z13 open which is the smoke alarm next to the faulty keypad. I popped the top off and it has clearly had water in it. I suspect the bathroom above had a leak at some point and did for them both.
Because of the open fault on Z13 I can't go any further. I have ordered a new detector and keypad but can I link out Z13 with a wire or resistor?
Thanks again I am chuffed it lives.