My dryer will sometimes fire up for a couple minutes and then shut down and not light again. Other times it never lights at all. I have replaced the igniter and the flame sensor. The igniter does glow and try to light and their is gas to the appliance. I think it must be the gas valve or coils on the gas valve. I removed the coils and the shafts in the center do not move at all. Should they? Thank you for your help.