If the water tank is empty, the error message ‘E1’ is displayed. If the water tank is filled without removing it, the error message ‘E1’ remains. You must switch the appliance off and on again to reset the error code. You can also simply remove the water tank to fill it, in which case the error message will also disappear.
This can also be found in the operating instructions on page 90 (U400 and U400+).