Visonic Powermax Pro - Installer Mode not visible

[NiToNi]

I just picked up a second hand panel on eBay to replace the faulty one I already had.

However, the Installer's menu ("Installer Mode"), which typically is visible as an option at the end of the User's menu ("User Setting"), is not there! After "Scheduler", it toggles back to "<OK> to exit".

I have performed a hard reset using the EDF jumper a few times but to no avail.

Any tip on how I could get into the installer menu because the panel's pretty useless otherwise...