BOSCH DW burned plastic smell, common problem?

We bought a BOSCH DW last year and about two months before the guarantee expired the thing started to smell terribly like molten plastics during the heating phase for water and especially for drying. It seems to emanate especially from the black plastic lining on the back of the unit. We never had any problems before. Called the "engineer" who came round and woffled about the heating element that needs changing. Why? Needed some money I think. Probably just a thermostat problem. Anyway, don't know what he did, I wasn't there. He left. Same smell. Next engineer fumbled around, left, same smell. Guarantee now expired. Still smells. Any poor connection problems perhaps to a NTC element somewhere perhaps?
I read that others had the problem but I don't want to accept that it is normal as it didn't do that before. I will test-wash with a datalogger inside to get an idea of the internal temperature...