Zanussi DE6744 stopping mid cycle with flashing lights, then not filling

I have a Zanussi DE6744 which stops mid cycle. The program and cycle indicator LED's flash together simultaneously. The manual says it could be a blockage, I have checked the water inlet filter and cleaned out the filters etc inside the machine. If I reset the machine by holding the program button in and powering it on I can restart the program, but it doesn't take on water and so just stops again. If I leave the machine on it's side overnight (has to be a good few hours)it then works OK for a few weeks until the same thing happens again. Does anybody think it's something blocked in the drainage system, does anyone know how I can check that out? I wonder if there is some congealed fat somewhere.. Any suggestions would be welcome. Thanks
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