I never opened up the ones I used, but I would expect that there is a similar heating element which just has no direct contact with the water and is connected to the bottom plate thermally, but not electrically (compare this wikimedia image.
I never opened up the ones I used, but I would expect that there is a similar heating element which just has no direct contact with the water and is connected to the bottom plate thermally, but not electrically (compare this wikimedia image.