So you started with a fault, replaced it, and still have a fault......?

Ahh, but that was a different fault. Original panel was refusing any codes except the user one, a SAB\Keypad tamper on setting, and refusing to default. All that after a mammoth power cut, which they appear to have form for.

 

This "new" one was failing to detect all the ID biscuits, because the wiring wasn't up to the published ID spec. Mostly unshielded, a star-wired config, and not a capacitor to be seen. Anywhere.

 

However, adding the "decoupling"-type capacitors to two of the run ends that I've found so far has worked, all the zones are showing up correctly now. SUCCESS! I'm going to do some soldering and put some short flying leads and heatshrink onto the capacitors (not the biscuits), make them easier to site within the detectors, then add one at any dead-end I find. Which appears to be every PIR and door contact.

 

Thanks for the advice so far, it's been useful to bounce ideas around.