The engineers at presto had a delicate balancing act. Too hot and it could start a fire. chances are you were trying to make more than a half of cup of popcorn and live at an altitude greater than 2000’. In addition to the thermal fuse a thermal switch was installed to prevent overheating. All testing for Presto was completed in EuClaire Wisconsin (low Altitude). My 10 yr old daughter tested ours out at many different altitudes and found that the fan they installed only works as designed in denser air (low altitude). If you live in Denver Colorado or Park City Utah a half cup is all you’ll ever get out of it before extensive cooling is required.