Open the front door of your Bosch Nexxt dryer to gain access to the drying drum within.
Grab the drum with both hands, and turn it in either direction. Use the panels that extend from the inside of the drum as hand holds, and apply pressure until the drum starts to move. If the drum moves with little effort, the drive belt is most likely worn. If the drum moves only with great effort, or not at all, the belt is likely in good shape.
Remove the top, side or rear access panel from your Bosch Nexxt dryer to visually inspect the drive belt, if the drum test in Step 2 leads you to believe there may be a belt issue with your machine. Follow the manufacturer's instructions to remove the access panel, as each Nexxt dryer model has different access panels, and require different steps for removal.
Visually inspect the dryer drum and drive belt. The belt should lay snugly against the sides of the drum with little or no play. The belt should be without cracks, splits or damage. If any damage or slack are visible change the belt.