When i turn the dryer on the burner will light

Hello, This problem is going to be your safety valve coils...basically they get old and over time of heating then cooling develop a short when they heat up...It may appear the gas lights to start but then goes out until the safety valve coils cool back down. Here is a picture of the coils This The coils are mounted to the gas safety valve, This should solve your problem. Hope this helps, Please feel free to comment again if you have any further questions or concerns. Good Luck! Mike