The most likely cause is thermocouple failure if you give me the model number of the stove I will be glad to find you a replacement here are the instructions for replacing it:
Turn off the main gas supply feed valve that supplies the oven. The gas feed valve is located on the main gas pipe that serves the oven regulator gas valve. Turn the valve so that it sits perpendicular to the pipe.
Locate the gas regulator valve at the back of the oven. Follow the gas pipe until the pipe connects to a square shaped metal unit, the regulator valve.
Locate the copper-tubed thermocouple that is attached to the regulator valve. The tube trails into the oven body and is attached to the regulator valve by a small nut. Unscrew the nut with a small adjustable wrench. Pull the copper tube out from the regulator valve.
Trace the copper tube into the oven body. The thermocouple head is at the end. The head is affixed near a burner with either a gravity clip or a clip that has been screwed into place. Determine which type you have by looking at the base of the clip. Use a flashlight to fully illuminate the area. If no screws are present, pull the thermocouple head up and out. If screws are present, unscrew the screws with a small screwdriver, then pull both the clip and the thermocouple head out of the oven.
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