After some time of pondering I finally figured out that the temperature switch is actually something pretty elaborate. The principle depends on little metal disks which snap-bend when temperatures near 100 C are acheived. Pretty neat. These sappers then push little tumblers which in turn cut the power to the kettle. On the picture you see two disks which were pressed agains the boiling element. There is also a switch in the handle, we’ll see about that in a minute.