Hi and welcome. You posted your question in the DD/DS603 series section, but code U3 is usually seen on a DD/DS601 or DD602 series. When this code appears, most comon cause is that the machine is set in LP or LOW PRESSURE mode and needs to be set to HP or HIGH PRESSURE. The fault is sensing water level too high in the drawer, which can also be caused by a blocked drain or inoperative pump. I can tell you exactly how to tell if the machine in in the wrong mode if you can tell us the correct model number. The machine's pump/drain system can easily be checked by putting the machine in diagnostic mode and running the drain pump.
I have F&P freestanding dishwasher the top draw has started to leak. I have checked plastic...
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I have F&P freestanding dishwasher the top draw has started to leak. I have checked plastic water pipes at the back they are fine. I think there could be a blockage but don't know where.