Automatic cut off on a kettle

 

The lab kettle has a cracked lid and is taking a longer time to turn itself off. I know that the electrical cut off is to do with steam so after the pan boiling adventure this month I wondered if it was to do with the pressure of the steam being reduced by the crack. It turns out that it is to do with steam, but that it is a temperature thing. The steam travels down a pipe to flip a bimetallic strip in the base which then turns off the power. It is explained properly here . In this case, steam escaping through the crack means that less is directed down the pipe so it takes longer to reach the required temperature.