I hope this helps as I managed to do it last night,
Makesure that the alarm is in Day Mode with the day and power lights on.
Press the Prog button (All indicators show)
Enter the engineer code
Press 1 (Zone 1 and Zone 2 indicators show)
Press 0 then 1 (this is for 10secs, 0 then 2 for 20 etc..., once entered the alarm will return to the programming mode)
Now exit the engineer mode, this should have done it.
If this doesn't work here is a link to installation guide for your alarm http://www.guardianalarms.net/home_security_manuals/ADE/Accenta_8_Installation_Manual.pdf
Page 13 is the one you need.
Hope this helps
Kevin Ladhams
November 2007