peter wrote:
So I guess I need a new kettle then?

Why bother? Just boil it a few times until the black stuff
stops falling off.


I had only used vinegar (hardly very acidic compared with limescale
removal acidic sachets?) a year ago to remove limescale.

It's probably not that, then.

Other than buying a different kettle, what tips are there to remove
limescale in the future if acid could cause the metal plating to
corrode?

Why bother? Just rinse it out every so often, and make
sure any gauze filter is clean (use vinegar, conc. HCl,
or etc).