p1. 1st use a test butt to call the no, from the line block nr controls, does it work ?
note adsl, star services or all manner of stuff will prevent your digi from working
p2 set up restore options correctly
p3 as above
& I bet you thought I was taking the piss...
probably needs battery's, however the unit may have failed, or just require relearning.
Personally I recommend trying to nail your installer down on a price to replace all battery's
as here's a scan of the factory fault finding guide-
1. Cable of each pair + Voltage of powered detector
2. Your doing this when the mains is removed ?
3. Your SDP will then be "final exit"
4. BSIA
5. Make something ?
I nearly bought a scope some yrs back to fault find a CCTV job, they used to be very expensive CRT things.... But now a few a thundred quid.
I'd love one but have no practical use for it.