The very first time you switch on the radio it does a default automatic scan of DAB stations to set it up, and all the stations are then stored to memory. Therefore it doesn't need to scan each time you switch on, as it already has the information it needs.
If you feel that you actually require a new scan because you've lost access to some stations (maybe because you're operating the radio in a different area to where you were when it carried out the initial default scan), or you're not able to pick up a new station that you've heard about for instance, then you have to start the Autoscan yourself by simply pressing the Auto Tune button while the radio is on the DAB Band.
Kshaky
November 2012