How do I remove limescale from a kettle?
Limescale is calcium carbonate left behind when hard water evaporates. It is harmless to drink but insulates the heating element, so a scaled kettle takes longer to boil and uses more electricity, and flakes eventually end up in drinks.
Acid dissolves it, and household acids work perfectly well. Fill the kettle with equal parts water and white vinegar, or water with the juice of a lemon, bring it to the boil, then leave it to stand for around an hour. Heavy deposits may need longer or a second round. Afterwards, rinse thoroughly and boil with fresh water once or twice, discarding it, to clear any residual taste.
Citric acid powder is the tidier option and is what most commercial descalers contain. It leaves no smell, which vinegar does, and is inexpensive.
A few cautions matter. Do not scrape the element with anything abrasive, since damaging the coating shortens the kettle's life. Do not use a stronger acid than needed. And check the manual for kettles with a plastic or coated interior, as a small number of manufacturers advise against vinegar specifically.
Frequency depends entirely on local water hardness. In a hard water area monthly is reasonable; in a soft water area it may never be necessary. Descaling as soon as a film appears is much easier than removing a thick layer.
Prevention helps. Emptying the kettle rather than leaving water standing reduces deposit substantially, since scale forms as water evaporates. A mesh descaler ball placed in the kettle collects scale that would otherwise coat the element, and is simply rinsed occasionally.