On Saturday, 5 September 2020 08:33:00 UTC+1, JohnP wrote:
Curious - a tap in our bathroom (Roca)stays very shiney. One in our
downstairs loo (unbranded) suffers from limescale marks and needs a wipe
with vinegar almost daily to keep it shiney.

What could be different?

Try wiping something like vaseline onto a clean dry tap. (It is actually best of the vaseline is thinned but you might not want to use paraffin or petrol.) Leave for hours. Wipe off and then apply car wax (or pretty much any other wax).