sediment can cause a problem but shouldnt cause it to overheat. Overheating can be caused by a heating element shorting to ground and thus staying on all the time, but most likely the thermostats are at fault. check the elements for short to ground. check resitance of each element, should be somewhere between 8-15 ohms; if both elements okay, replace both t’stats… they are relitively inexpensive…..if you dont know how to check the elements call in someone who can. Good Luck…