If it glows continuously, it's a bad flame sensor, Part # 338906
. If it glows off and on, it's bad gas valve coils, Part # 279137
. A dryer will not turn itself off in the automatic cycle if there's no heat.
Part # 338906
Flame Sensor, AP2910747
Part # 279137
Coil Kit for Dryer Gas Valve (3 Coils), AP3094108