Dryer runs (without heat) only by holding down Push-to-Start switch.

Dryer runs (without heat) only by holding down Push-to-Start switch. It won’t even stay running with Air Fluff (no heat) selected. The thermal fuse has continuity. The machine does not respond at all to Kenmore’s "Diagnostic Test" for factory service personnel. I’ve read some of the blogs saying the problem could be motor relays, igniter, sensor, thermister, gas solenoids, even the timer and/or the microcomputer, etc. For the last few months the timer would run fine except it wouldn’t complete the cycle and run to the stop position.
I would appreciate help in narrowing the possibilities.
Thank you,
Reinaldo

Some how, I posted my concern in the wrong forum. It should have been in the dryers forum.