I agree with letting it steam itself out. Fill it with vinager water (1/4-3/4) and set the iron on a folded cotton towel with the steam button pushed in. Let the iron just sit there and go through the entire tank. Do this a couple of times. And when you do start to use the iron, use a pressing cloth for the first several times. Hope this helps.
OH - - you might also want to check with the person qwho takes care of your sewing machine. Most of their techs can also work on irons. Although if the iron is just a regular iron and not one of the really expensive ones, it might be worth it just to pitch the irohn and buy a new one. With me I would probably just buy a new iron and see the $$s as the price for my sanity.