Gas Dryer Thermostats

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

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.

Limit Thermostats

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.

Procedures for Checking Thermostats

Disconnect the power cord.
The operating thermostat for a GE dryer is mounted just behind the lint filter and down under the door. You will have to remove the front of the dryer to get at it.
For a Sears or Whirlpool dryer, move the dryer far enough away from the wall that you can disconnect the dryer vent hose.Remove the 5/16" sheet metal screws securing the rear access panel. Save the top, middle screw for last. Set the panel aside.
Set your ohmmeter at its lowest scale and confirm that the thermostats are closed by measuring less than 1 ohm. Replace them if the ohmmeter shows an open circuit at room temperature. The thermostat's operating temperature (temp that it will open) is stamped on its base. An L155 thermostat will open at 155 degrees. If you want your dryer to operate at a higher temperature, replace its operating thermostat with one bearing a higher L number.
Perform the same checks on the limit thermostat as for the operating thermostats in the preceding step. You should have smelled the problem with a failed limit thermostat. A limit thermostat will not cycle unless the selected operating thermostat has failed closed. If the dryer is operating on the limit thermostat, it has transformed into an oven and is baking your clothes in a convection chamber at a temperature of about 250 degrees! You can order a replacement limit thermostat using the model number of your dryer.
Take all suspect thermostats to your nearest appliance store and purchase new ones. If you are replacing one of two operating thermostats, determine from the wiring diagram on the back of the dryer whether you are replacing a high (Cottons) or low (Permanent Press) temperature thermostat. Or If you had two operating thermostats and one was charred beyond recognition, copy the numbers off the one that checked out OK and purchase the other one from the parts list. Take your dryer model number along.
Replace the thermostats (you can reverse the wires on a two-terminal thermostat with no ill effects).
Replace the rear access panel or front panel and check for proper operation.