My old guru, AT1 Crowe, used to tell me, "Look, sailor, how you gonna even begin to troubleshoot equipment to figure out what's wrong if you don't know what right is?" Applying this flawless logic to gas dryers, if the burner in your gas dryer ain't firing up, you gotta at least start by knowing what the correct operation sequence is. Grand Master Reg lays it out for us:

normal operation ..

1) Ignitor glows

2) various clacks ... Gas Valve opens and Ignitor stops glowing

3) Gas and Flame stays on until Dryer heat rises to about 160F, then goes off

4) Flame stays off until Dryer heat drops to about 135F

repeat