The dryer does not heat up at all.

If the fuse is good(continuity) and the dryer control(cycle) thermostat is also good then you should have power going to the gas valve assembly when the machine is running unless the timer is in the no heat or wrinkle free/cool down mode. When the gas valve assembly is energized the flame sensor

mounted outside the burner chamber detects the heat from the ignitor. When the heat is very intense then the sensor shuts down the ignitor



and that frees up the power so that the coils can be fully energised and open the gas gates. The gas comes out and hits the red hot igniter and you have ignition. It stays on for maybe 2 or 3 minutes or until the control thermostat is satisfied and shuts down power to the gas valve assembly. So...
If your gas dryer has a good flame sensor and a good igniter AND the dryer will work some and quit, replace these:



The coils get hot and quit on these machines when they get a little age on them. It is aggrevating because it is a hard to diagnose thing. But well worth the 20 bucks.

As you can see from the above photo all them coils is wired into the same circuit so why wont they open and let the gas out while the ignitor is glowing? Simple: The ignitor is using all of the amperage in the circuit. The coils just don't have enough to open but they do carry the current. The flame sensor has a bimetal in it that opens and it shuts off power to the ignitor. Then the only thing left is the coils in the circuit and Kawooosh Houston we have ignition!!!! :D The flame only stays on 3 or 4 minutes or till the drum gets hot as hell and then the control thermostat mounted on the blower housing shuts down the power to the gas assembly. The drum keeps going till the heat is needed once more to maintain drying temp and then power is once again applied to them coils. This continues till th timer gets to end of cycle. Should the control thermostat get stuck and NOT shut down then the fuse next to it will blow and you won't have any power to the gas assembly, but the dryer will still run.