Depending on severity of the accumulation of the lime/calcium and mineral deposits it may not come off completely. It will require a mild acidic cleaner like
or "Lime Away" providing the dishwasher tub is
to disolve the calcium. You could pour vinegar directly over the heating element and let it soak for a few minutes and repeat, and then run a short cycle with 2 cups of vinegar only in it. If the element is coated with a thick layer of the calcium and mineral deposits the heating element may need to be replaced.
NOTE: Do Not Use vinegar or "Lime Away if the tub is Stainless Steel
. Using vinegar or â€œLime Awayâ€ on a stainless steel tub will cause the stainless steel finish to dull. There is a product that can be used safely in Plastic tubs and Stainless steel tubs called "Dishwasher Magic" part# WX10X10200. It can be ordered at Sears.com and click on Parts.