I soaked the top of my teapot in 50:50 hot water and vinegar to remove hard water deposits. When that wasn't enough, I removed the screw inside the lid that held the "whistler". This was aluminum and still was a little roughness on the underside from deposits. I scrubbed it with non abrasive dish scrubber and the hot water and vinegar. I paid special attention to the edge where the cut outs were to make it whistle. When I replaced the aluminum piece, I lined up the cut outs with the holes on the top. I found I had to tighten the screw to slightly less than tight There needed to be a little room for the piece to vibrate. It worked fine after that.