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E15 error in your Neff Dishwasher indicates that water has leaked in the base of appliance and activated the anti-flood device.
You will have to unplug the dishwasher and pull it out.
After that, tip it backwards by around 45 degrees and make sure excess water drains off completely.
Also check the water inlet valve and drain hose, make sure nothing is clogged.
Now plug it back and check if it works.
Let me know how it goes.
If you need further assistance, please get back with the complete model number located on the label inside the door or on lower front panel.
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