Easiest way to rid that kettle of nasty scale, is to never have scale in the first place. I used to have to descale once a week or two w/o fail. Really hard "well" water here. To descale, I just put vinegar in and let it sit a while, slosh it around, pour the same vinegar into the next thing to be descaled ... and rinse at least several times.
In order to avoid ever having to descale, get a GraviTea water purifier or similar. Since I began using this, I have not had to descale anything for the last 14 months ... life is good w/o having to descale!!!