The water does not foam anymore at the lavatory faucet? Would limestone play tricks?
Cut the end of the neck of a plastic water bottle.
Opt for a long and rather narrow neck, like Quézac.
Engage the end of the faucet into the neck closed by the cap.
Hold the assembly in place with tape.
Pour some lukewarm vinegar into the improvised cup (the end of the tap should be fully soaked).
Note: the removal of limestone in the frother is faster with warm white alcohol vinegar.
Leave on for one night.
Complete the cleaning with a sponge loaded with baking soda to make the sink and the faucet shine.
Wipe with a cloth.