Learn how your appliance is supposed to operate so you can determine if it is malfunctioning.
The temperature of the air inside the drum is regulated using thermostats. Thermostats open and close an internal switch with respect to the temperature of their environment.
All the thermostats do is allow power to get to the gas burner assembly. If it is receiving any power, the thermostat(s) must be doing their job. If a thermostat were to fail (or even open normally for cycling the temperature), they would prevent all power from getting to the burner assembly, also stopping burner's ignitor from glowing.
Operating thermostats control the temperature of the air inside the drum. You may have one or more operating thermostats mounted on the exhaust side of the blower housing. One may be used for the "Normal" drying cycle and will open at the highest temperature. The thermostat for "Permanent Press" or "Gentle" will open at a lower temperature. The operating thermostats provide 120 volts to the burner assembly to demand heat. Operating thermostats normally open from 120 to 170 degrees and are always closed at room temperature.
I have seen operating thermostats in a gas dryer shift their operating temperature down with age. This will cause the burner to "short cycle" and the clothes will take longer to dry. A "cool" thermostat will check out fine with your ohmmeter. If you suspect that your operating thermostat opening temperature has shifted down, replace it with a new one with the same "L" number.
The limit thermostat is located on the side of the burner funnel.
As its name implies, this thermostat shuts off the burner assembly if a dangerously high temperature is reached. This can happen if the operating thermostat fails (welds closed) and demands heat constantly. When this happens, the limit thermostat becomes the operating thermostat. Unfortunately, the limit thermostat cycles at a temperature almost 100 degrees higher than the high temperature operating thermostat! This does your clothes absolutely no good. You should be able to smell that something is wrong.
All of the information in these Appliance Clinic procedures is provided FREE OF CHARGE. No liability is assumed by the author for the accuracy of the contents or damages caused by the use of these procedures.