Air flow
My mother in law went through 3 toaster ovens in a very short time period. She used all the time. I had to find out why her toaster ovens kept burning out. Here is what I found. She used bakeware that was to big. Meaning it fit in her toaster oven but it didn't allow for airflow. Your bakeware should not touch the oven walls. When we replaced her bakeware with toaster oven size bakeware it fixed the problem.