My kettle becomes very noisy when it boils. I live in a hard-water area, so I regularly treat it to remove the build-up of . For a few days it then seems much smoother and quieter. What鈥檚 going on?
鈥� I assume you refer to simmering, the noisy stage of hissing or 鈥渟inging鈥� when water explosively forms steam bubbles against the heating element, but the surrounding water is cool enough to implode the bubbles quickly after they form. That cyclic process produces the sound, with the kettle body acting as a soundboard. If you are unsure that this is causing the noise, gently slosh the water in the kettle back and forth when the noise starts. If it really is simmering, sloshing interrupts the noise until the proper, comparatively quiet, boiling gets under way.
In a clean kettle, heat passes efficiently through the heating surface, rapidly completing the simmering stage, so singing soon stops. Also, a clean, smooth heating surface retains bubbles poorly; they detach while small and implode in the water instead of causing large impacts against the heating surface, so the soundboard produces little sound.
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However, limescale is a poorer conductor than the heating element or kettle wall, and a thick mass of scale accumulates heat before passing it on. Accordingly the simmering starts slowly, but boiling starts even more slowly, so that the simmering lasts longer.
Jon Richfield, Somerset West, South Africa