Tappan -F1 error code

We have had problems with our Tappan oven during bake cycle since it nearly new. It beeps and displays an "F-1" error code and has to be reset. Sometimes it will complete the cycle and sometimes it will not. Sometimes it will not reset period. We delt with the problem for some time due to the cost of the part, (a timer unit) we were told was needed to repair it. Recently we replaced it and the part isn’t a week old now and the problem has returned. (It did work correctly for several bake cycles prior to the "F 1" error code returning) Has anyone experienced this same problem? Can anyone tell me what is wrong or how to fix it? I’ve checked the internet for Tappan’s web address to no avail. I assume they have been bought out by someone else?