The indicator light on my cooker

Here's the indicator light for my oven. The light is on when the oven is cold and goes out when the oven reaches the correct temperature.

 We made a similar device by putting a thermistor in a potential divider with a 1000 Ohm resistor. We then put an LED in parallel with the thermistor.

 When the thermistor was cold, the LED was on. The thermistor had a bigger resistance than 1000 Ohms and so took a big enough share of the battery voltage to light the LED.

When placed in hot water, the resistance of the thermistor went right down so it took only a small share of the battery voltage and the LED went out. I assume that on the oven , the fixed 1000 Ohm resistor is actually variable, set by the dial to give a different trigger point for each temperature.