The following link explains how to troubleshoot and dryer "no heat" problem and the common causes:
Read through the link thoroughly, paying particular attention to the section that discusses proper ventilation. Most dryer heat related problems are caused by insufficient air flow which, in turn, causes the dryer to overheat to failure. More commonly, the Thermal Cut-Off (TCO) fails. You will need to check all the components mentioned in order to be sure. If you haven't had your dryer ventilation cleaned or inspected in a while, now would be a good time to do so. Failure to correct any potential existing problems, can cause premature failure of any parts you replace.
If you have questions, or require additional assistance, please let me know, so I can provide you with a viable solution. i hope this helps you.