Bet this didn't just happen that all 4 have suddenly stopped regulating. More likely that one or two have been doing it for a while and you put up with it or used the other elements. Now they have all packed up. Behind the knob on the panel is a simmerstat control switch. One for each element. They will have to be replaced with new ones. You can't repair the old ones they are sealed units. Not going to be a cheap job doing four at once. Next time replace them one at a time when they first play up.
Lincoln Appliance NZ, April 2012
