Since no one else around here seems to have any helpful ideas for anyone, I will chime in here, as I now have a little experience of my own. I am not a professional, but I have been through my own issues recently, and I picked up several good tips (not from here) along the way.

If the repairman replaced the entire gas valve assembly, this should have included new valve solenoids and flame igniter as part of the kit. It would be very unlikely that either of those parts are faulty out of the box, but I suppose anything is possible, especially if the repairman reused the old igniter and solenoids, which would be highly disreputable. First, make sure that the igniter is coming on by starting your dryer on a high heat cycle, and then watch for a bright glow coming from the lower left side of the base of your machine. If you see the glow, then listen carefully for a clicking sound that occurs within 2-3 seconds after the glow begins. If you see and hear both, then your igniter is working, and your valve solenoid is also working. It also means that your thermal fuse is good, and your flame sensor is working. You need to test the high limit thermostats and the running thermostats on the back of your machine to insure they are good. You should also clean your machine thoroughly. Vacuum your lint exhaust hose, the exterior vent door, and (if possible) remove the lint duct from the back of your machine and clean it and the blower wheel that is located inside. It may be possible to do this without completely removing the lint duct by using a series of extensions and fittings on your vacuum cleaner. Just do a very thorough job, as excessive lint buildup can cause the dryer to stop heating, even intermittently. If it's still not working, then you may have a bad timer or a bad control panel, which is pretty rare. There are videos available for testing these as well, should it become necessary.

Here are the steps that I would follow if I were you:

1. Watch these 2 videos (EXTREMELY helpful) so that you can adequately understand how to fully diagnose your issue and track down the root cause of the problem:
https://www.youtube.com/watch?v=QP1Z4OWjTuA

https://www.youtube.com/watch?v=qGpojymCRNU

2. If you haven't already purchased one, go out and buy a multimeter so that you can test each component in the chain.

3. Most parts can be found at Amazon.com at a discount price.

Good luck!

This dryer doesn't have a thermal fuse nor a "running" thermostat and if the high limit was bad, the ignitor would not work at all. There's no rear access to this machine. This dryer uses a thermistor input to an electronic control board to determine temperature and then uses a relay to turn the burner on/off to regulate temperature. It also uses a moisture sensor to determine dryness of the clothes. You need to monitor the voltage to the burner to determine if the control board is turning the burner off or if something like the valve solenoids are failing.

Eric