Product review (5 stars): Saved me from replacing the dryer, for around $10
Like some of the other reviews, my dryer would heat up at first but after about 20 min. or so the ignitor would come on, but the gas valve would not open to allow the flame to continue heating.  Normal operation is the gas valve is turned on and off by these coils several times during the drying cycle as this is how a dryer maintains the temperatue for drying your clothes.  It is supposed to work just like your house furnace, when it gets to the right temp. it shuts off and then comes back on again when the temperature drops below a certain point and will cycle like this until the timer runs through the whole drying cycle.  Well after mine heated up and ran for a while, 2-3 cycles on the gas valve, the coils became hotter and would not be strong enough to turn on the gas valve.  So I did like another person did and researched the internet and found that this appeared to be a common problem for gas dryers.  It makes sense once you think about how many times it is required to cycle on and off for each drying cycle and the fact that it gets pretty warm where the gas valve is.  So for under $10 including shipping, I replaced the coils in less than 10 min. (I had already cleaned the dryer inside when I was troubleshooting the problem before) and we were back in business and saved myself $150 on the repair for not having to call a repair man and be charged labor and inflated cost for the coil kit.  Or I could say I saved about $900 from just going a getting a new dryer when I really didn't need one.  I hope you find this review helpful as I did not completly understand the operation of the gas valve until I did the research.