Another one ......

Notice how kettles get that "scale" inside them!

Well, natural cleaning is half white vineger, half water - bring to the boil.

Let stand until COLD ...................... tip out the water and VOILA!!
If REALLY, REALLY DIRTY - REPEAT!!

P.S. Just a side note, your house will smell like vinegar for about 2 hours afterwards. So maybe boil the kettle OUTSIDE!!!