zanussi dce 5655 help please

not sure if im on the right forum here.
ive been in the trade of repairing appliances since 1984, come out of it in 1999 and returned to the trade again, so just finding my feet.
i have been to a zanussi 5655 three times, suspect it was leaking and tripping the flood microswitch, as there was signs of some water there. fixed that and customer has reported same fault. aagghh.
symptoms; after half an hour through the cycle, the red light flashes and the machine does not go any further.
however, i didnt find the fault because everytime ive been to the machine it has worked.
an intermittent fault.
can anyone shed light and maybe point me in the direction of where i should be looking? i thought about the heater, but if it had gone it wouldnt work some of the time?
any help would be appreciated. i have lost out on this call, i have been three times, i just want to keep the customer happy as she has been coming to me for 15 years. t.i.a.