How to factory reset a Marshall CODE 25 or CODE 50 Amp
To perform a factory reset on your Marshall CODE 25/50 amplifier and return it to the factory settings, you will need to power of the amplifier first. Once it is powered of, press and hold the "AMP" button while powering on the amp. Once you see the confirmation screen on the display saying "Presets reset", press and hold the "STORE" button to confirm the factory reset. You can press any other button to cancel the operation.