Diagnosis
No heat on a gas dryer is almost always an ignition failure. The gas valve opens but the igniter doesn't light the gas.
How to Fix It
Check the igniter first. Unplug dryer. Remove the front panel. Locate the igniter (glows orange) near the burner tube. Look for cracks or breaks. Test for continuity with a multimeter. Resistance should be 50-400 ohms. If open, replace the igniter (part # 310241).
If That Didn't Work
Next suspect is the flame sensor. It's a small rod near the igniter. Clean it with fine steel wool. If the igniter glows but gas doesn't light, the gas valve coil or pressure regulator could be faulty.
Heads Up
Gas work is for qualified techs. If you smell gas at any point, shut off gas valve immediately and call a pro.