This happens when the ceramic insulating material which surrounds the heating element inside the hotplate begins to fail. May be a sign that the ceramic is breaking down and the offending plate(s) need to be replaced, or could be due to dampness after being unused for a prolonged period. If dampness is the problem, you may be able to alleviate the effect enough to bring the plate back into service by simply heating it - e.g. by standing a hot pan on it for a while.
Me, April 2010
