Kettle
Limescale in a kettle won’t kill you, but it’s certainly unpleasant. Citric acid will reportedly descale a kettle better than any other product.
All you need to do is pour about a tablespoon of citric acid into your kettle along with some water.
Use enough water to make sure the entire element or base plate of the kettle is submerged.
Turn the kettle on and listen to the citric acid fizzing as it reacts with the limescale
If the fizzing stops and there is limescale remaining, then repeat the process until all limescale is removed.
Pour the water down the sink and rinse the kettle thoroughly twice before boiling a cuppa.
source: express.co.uk