It may be coincidence that the final exit door contact has developed a fault at the same time as you changing the code.
More likely is that if you used the engineers side of the programming to change the user code and may have inadvertantly set the exit time to 5 minutes or similar.
If you have access to the engineers programming you can adjust the exit timer - press 1 (Zones 1 & 2 will light) enter 02 for 20 secs or 03 for 30 secs.
Alarm Engineer Bristol
November 2007