Dryer won't heat up consistently, automatic cycle timer won't advance.

Timed dry setting will advance but dryer still won't heat up every time I start the dryer.

I tried resetting the circuit breaker, works sometimes to get the dryer to heat but automatic cycles still won't advance.

Any suggestions as to the problem?

Gene,

I appreciate the advice, I checked out all the vents and the blower wheel is working fine (I even vacuumed all the extra lint from all areas).

Still having trouble with the dryer heating up, should I check the timer since it won't advance or heat up?

Thanks