There are white or rusty spots in my Philips Avent Bottle Warmer

If you have white or rusty coloured spots in your bottle warmer, your bottle warmer has limescale build-up. Clean or descale your bottle warmer to remove the spots.
Note:  we recommend descaling the bottle warmer every four weeks to ensure that it continues to work efficiently. In hard-water areas, more frequent descaling may be necessary.