Gas Dryer (Amana) stopped heating after 5 minutes

My gas dryer (Amana) stopped heating after it ran for about 5 minutes. After that the drum still turns, but there was no heating.

I tried to clean the venting pipes and finally pull off the venting pipe from the gas dryer and turned on the gas dryer for 50 minutes. This made no effects. So I assume this is not the venting pipe issues.

Any idea what can I do to fix it?
Thanks in Advance.
Max:(