Unplug your dryer and shut off the gas valve at the rear of the unit.
Pop the access panel on the bottom of the front of the unit off to expose the internal components of the dryer. If there is no front access panel you will need to access the internal components via the rear panel of the dryer.
Remove the screws on the back panel of the dryer, as well as the top cover of the dryer.
Lift the top panel off of the dryer and remove the back panel. The heat sensor is a small metal rod mounted next to the burner assembly. The burner assembly will be located near the bottom of the dryer, next to the dryer tub.
Check the wiring where it plugs into the base of the heat sensor. Unplug it and plug it back in, making sure it is secure. This should fix any wiring problems with the sensor. If the rod of the sensor is cracked or damaged the sensor will need to be completely replaced.
Unplug the sensor wiring and remove the screw holding the sensor in place.
Remove the sensor and fit a new one in its place. Replace the wiring and screw.
Replace the panels of the dryer.