If you live in a hard water area, you’ll have limescale, and the build-up of this is one of the main reasons kettles break down. When the metal element gets coated with scale that inhibits the heat getting into the water, which may cause it to overheat, reducing its life.
To overcome this you should descale the kettle about once a month. Fill with half water and half clear vinegar, making sure it comes up over the scale line, and bring to the boil. Switch off and leave to cool until the fizzing stops.
Another idea is to put a Cadnit inside your kettle. It’s fine stainless steel wire coiled into a ball that provides a large surface area for the scale to collect instead of on the heating element.
Next time you buy a kettle, get one with a built-in water filter. It’ll improve the taste of your tea, get rid of scum and reduce limescale build-up.
Other things you can do: empty and rinse before refilling with fresh water each time you boil (helps get rid of loose scale); boil only as much as you need; pour away any surplus water before it cools; empty the kettle each night.