The Element itself wil not be rusting and in the Bifinett the element is not exposed, I would suggest your water supply is carrying water born rust which will build up on the bottom inside of your kettle, This rust and deposits can be cleaned with Citric Acid crystals 1 teaspoon with about half pint of water(maybe your Chemist will supply the Citric Acid) just boil in the kettle and it soon clears the deposits away.
On the subect of kettle busting into flames I have had a similar problem caused by over filling the kettle which then allows water to over flow to the base of kettle and onto the power base shorting the power base with a few sparks etc.
before blowing the fuse.
Happy Brewing
Barn Owl
October 2009