I dont do all grain but a friend does and hes running into issues.
He did a few sugar wash's and had great success but has now moved onto Rye all grain wash's and keeps burning elements.
The setup is 100L boiler (FSD) running 2 x 2400W twin tube heating elements (FSD) both on controllers FSD kegland)
Heres a pic, elements were clean before the run and the one on the right has been cleaned a little to show comparison.
Cheers