my daughters integrated washing machine EWX14440W (Electrolux) hot water?

My daughters integrated washing machine EWX14440W (Electrolux)no longer will heat water for warm wash. 3 times the heater element has been changed, 1st by myself worked for a while then same problem, thought it may be something causing element/ thermistor to go faulty so got engineer to fix. He said I had not located element in internal clips, therefore touching drum and causing fault. He fitted new element, problem fixed but faulty again just after warranty expired. I replaced 3rd time but no fix this time. I think there is an alternative problem causing heat element problem but could be wrong as I am not a white goods engineer, can u help please, Gareth Cridland