Try The Works, either shower/tile cleaner or toilet bowl cleaner. Don't soak it with the toilet bowl cleaner but both of these products helped remove some heavy build-up when we moved an office. I'm guessing you've already tried baking soda, CLR and/or Lime Away? While I'm not a big fan of heavy duty chemicals, they come in handy when less toxic methods fail.

It was free, just thow it back to the curb, where U found it!

moroseaz, thanks. I don't usually use chemicals, so I did not even think of that!

etienne, how wasteful! This is a perfectly good, sturdy kettle that has YEARS of use left in it. It simply needs a good cleaning. You and I would not be good friends, as I don't toss away anything that can be reused, recycled or repurposed, even if I have to give it away to someone else who will appreciate it. I used to be like you. I was one who threw the stuff to the curb, not one who dug through stuff others threw away, then I met someone who showed me that people toss out really great stuff, and off I went curb picking!

I've gotten antique furniture, a whole set of Revere Ware pots, and so much more. Down here in FL, when someone dies, the children don't want to be bothered with their old stuff, so they just toss it on the curb. You'd be SHOCKED what people throw away...or maybe not. I am sitting in my LR and I can see at least $100 worth of stuff I got from the curb, including the pole lamp I'm using to illuminate my laptop as I write this and a beautiful wicker chair that didn't need any repairs at all. That's not counting the plant pots, books, rugs, and more or the free La-z-boy recliner that was given to me by someone who wanted it out of her house because it was her ex-husband's.

I've used dip-it coffee maker cleaner available in the grocery store.