This is a tip my mum showed me and i am very grateful for it.
To remove Limescale from Kettle and hard water stains from kitchen sink basin, use 'Lemon Salt'.
Example: Put one table spoon of Lemon Salt in kettle, fill with water and boil. Will clean kettle and can use the same water to clean/remove hard water stains from the kitchen sink.
Super simple and works great.