Why does my Beko oven keep breaking?

I bought a Beko cooker 11 months ago, and it worked perfectly came back from holiday and the oven wasn't working but the hobs and grill were working, got Beko out and they said it needed a new thermostat. They fixed it and it broke again the engineer told us it is happens with this model of cooker all the time. So we requested a replacement. After 6 weeks without an oven we got a replacement, it was the same make but a different model. Argos had kindly given us one £100 more expensive than the last. The problems we only had it one day and the oven has packed in?? yet the hobs and grill are still working again? Is this just a problem with Beko or do you think there is a wiring fault connecting to the cooker or something else?