Our manual says to add some citric acid to the water and run it empty. It’s just a build up of something that’s in the water it’s not harmful at all.
Also if you used bottle water it doesn’t get that build up as quick as boiling water doesn’t get it out.

Good old citric acid , like a tea spoon or 1/2 teaspoon in water, it’s a great descaler I use it to descale the steam vaporiser

Everyone is different and have different opinions

Try the vinegar as suggested below

I’m sorry to say but i had on them and i threw it out. Only because it looked like the metal in the bottom was rusting and it was only couple of months old i found it was a big waste of money and used a pot with water and sterilized my bottles myself

Awesome thank you

You can buy kettle descaler from a few places. I believe woolies sells it. Try the recommended amount for your sterilizer and it should work fine. Reminds me I must do it myself!

I use white vinegar on mine when the build up gets to much. I simply fill with the vinegar and leave for half hour, tip out and wipe out with a damp cloth.

Where do you buy that from?

I use Descale Magic. Just make sure you check the manufacturers info before use.