Siemens SE25A090 Dishwasher - Heating Element Fails Every 4 Months!?

The dishwasher heating element fails and has to be replaced every 4 months! The dishes are rinsed to get off any large bits of food before putting them in it. Also the water softener is used and kept topped up with salt (although kept on a low setting as the dishwasher tablets contain salt). It seems strange that each element always lasts the same amount of time. Is there anything else that may be causing the elements to fail?