On 27/12/2017 22:43, Chris Hogg wrote:
If you live in a hard water area, then deposits of lime may have built
up on the discs. Soaking them overnight in vinegar may be all that's
needed.

Failing all that, simply buy a whole new pair of cartridges.

Assuming you can find somewhere that sells the oddball type of
cartridges that your taps need. There are quite a few variations.