Over the last few years I have lost 2  Le Creuset hob kettles by using light "Recommend" cleaners in short they would after a few days of using the cleaner ( As we know calcium builds on the inside very quickly) I noticed the inside would rust and make the kettle redundant. These kettles cost £73 pounds each. Anyway I now have a Steller stainless steel kettle very nice indeed and I am sure all you ladies know this but I found if I fill the kettle over the calcium watermark bring to the boil and add a whole lemon cut up, Leave overnight.The next morning a quick run around inside whilst the lemon water is still there with the nylon plate brush and the kettle is as good as new with no damage. Another tip is do not leave any water in the kettle after you make your cuppa etc.  :D