Actually, going in to diagnostic mode is not always the best way. Some engineers that have some experience may do this, but if you are not careful, you could also enter the wrong thing and lock the system. Additionally, resetting the unit to factory default will also erase your configuration.
With the new AS/AX & DX units, there is no need to reset the unit to factory default anymore and many customers are not aware of this.
The password can be reset safely without loosing your configuration, but you will need to contact the Quintum Technical Assistance Center to do this. It is best to contact them during normal business hours (Monday through Friday from 8:30am till 6:00pm EST).