I have a dryer about 8 years old. I thought the heating element was bad and I replaced it. I found out since that the element was fine. So were the 3 thermostats. There is no clog with any lint and every thing seems to work on the thing just no heat. The breaker also is OK. Any suggestions.

Maybe no lint in the venting hose, but have you removed the cabinet and cleaned the blower and blower housing? Also you will have an air inlet and outlet screen that get clogged eaisly. Also check and see if the blower is working inside the unit