Gas dryer won't heat up. This occured just on a normal day of washing.
Can you tell me what part and the part number is to repair?

Here are the components involved in the heating circuit in your dryer: The timer; thermostats; igniter; radiant sensor (also called a "flame sensor"); gas valve coils.

You need to systematically check each one of these components, so that you don't waste money on unnecessary parts purchaces.

You can eliminate some of this testing by observing the igniter. Does it glow, when you have the dryer set in a heat mode? You may be able to see the glow from under the dryer, if you can darken the room. If you do see a glowing igniter, you can surmise that the timer and thermostats are working properly.

Tell us what you find.