Thanks for advice.
Checked and rechecked the cover, looks fine, and working correctly (red beam lights).
Still no joy. i'll call an installer but only as a last resort, but thanks anyway.
Replace batteries for all detectors.
I get the below messages when trying to set my i-on 16 alarm.
CANNOT SET:
RADIO SRN 01
SRN01 Superv Fail
Call installer:
KITCHEN
Tamper Z04
Tick to continue:
Battery v.low/missing
Any ideas?