A possible loose wire, loose part, burnt area, pieces of the dryer that have come off, fried or burned mechanical switches, etc. If the problem is not visual and you do not know what the issue can be, we recommend going here andposting an appliance repair questionto online appliance repa...
To test one, leave it in the dryer, power the dryer down, bypass the thermal device, and power up and run the dryer with it bypassed or jumpered. If the dryer now heats, you immediately know it’s open and should be replaced.
When you get right down to it, a gas furnace is just a box-shaped heater connected to some tubes. These days, they have added more internal complexity to make them more efficient, but all you really need to know as the installer is this:Cold Air in, Warm air out, Gas and Electricity...