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