Might not apply to you, but I have a Vista-50 system and you donít need the installers code to get into the programming mode. If you power off the system, then power on, and then within 30 seconds press * and # on the keypad at the same time, you get into the privileged programming mode.
In that mode you can then also change the installers code if you want. Donít know whether yours would be similar however.
(Iím assuming you have a manual so you can read out and interpret/change the data in programming mode Ė including House-Id,etc.)