Aside from the kettle not being too hot, or not aligned properly on its base or on a level surface, It's likely due to the bimetallic plate inside the switch which will have come loose or is not properly positioned. You can give the kettle a shake to see if that sorts it, or otherwise take it apart and look at the metal plate, make sure it's seated properly on the pin. If all else fails and you need this kettle, you can tape something heavy under the switch like a metal nut to give it more weight.
Rob
March 2025