The Kenmore 600 series gas dryer is not heating.

Assuming the gas is on, if the dryer starts but doesn't heat, the ignitor could be bad. Need to find the schematic for the dryer and test the ignitor. Could also be a bad high limit switch although in some models, nothing will run if it is bad. If the ignitor works, could be a bad gas valve sensor or a bad gas valve. I'd go with the ignitor to start.

These driers will do that when the lint builds up like concrete on the inside of the air ducts. You need to totally tear it down and scrape out and wash all of the parts except the motor, which you vacuum out. You can go to YouTube to see videos on how to take it apart, but do a very good job or it will fail again quickly. You may need to replace a blown thermal fuse which is near the elements. Check the different safeties to find the one that is bad; they are wired in series. I would get a new belt and change it while you have it apart and get some white lithium grease and grease any bearings you find. You need to clean out a drier every two years, at least, according to the manual. Another possibility is a bad door switch, but it's rare for them to fail. What you have to do is tear it apart and check all safeties and you will find the problem fairly easily with a good ohm meter. Check everything out before you buy any parts and never change a part without checking with an ohm meter to see if the part on the drier is bad. Good Luck. DrTom4444
\
http://fixitnow.com/2005/03/black-smudges-left-on-clothes-after.htm
http://dl.dropbox.com/u/8010163/Drier%20Service%20manuals.zip