Wirlpool cabrio f1 error help please!

Question

I am having a problem with our whirlpool cabrio elec dryer, showing the F1 error. usally after 38-45 min of use and it is intermittent. we had a tech already check it out and could find no problems. we cleaned out all vents, and still recieve this error. going crazy not knowing what to do. we have extended warrenty and only had it for about 2 months.please help!!