A friend's bath has a mixer tap with a circular sliding collar which, when one slides it downwards, activates the shower head. Unfortunately, the slider has stopped working.
We're in a hard water area, so I think the problem might be that limescale has bunged up the mechanism. My challenge, however, is how to remove the limescale from the internal workings without removing the whole tap from the bath (the bolts are all rusted to hell and taking them off would probably mean replacing the taps and mountings).
Any ideas on an effective, simple way of achieving this?