I have a 3 year old dryer that won't run. If I push the start button it runs until I let go. I also notice the gas heat will not start. I have checked the thermistor and thermal fuse as well as the high limit thermostat. Any ideas?

You have a centrifucal switch or a relay that is not latching for your hold circuit. To properly diagnose, you'll need the wiring diagram. If you can scan and post it, I'd be happy to look over it and give you some ideas.