Ret. :
My son has a standard kitchen tap with separate hot and cold valves on
either side of the tap. I took a look at it today because it has
developed a steady drip.

The valves are ceramic disc with a quarter turn to full off/full on.

I removed each 'cartridge' and took it apart. I could not see any
problem at all with the ceramic discs they did not appear to be
scratched or damaged, nor was there any grit present. The various seals
were in good condition.

After cleaning and rinsing all components, I put them all back
together, replaced them in the tap and............. drip drip drip!

Anyone any suggestions?

We also live in a very soft water area, where scale simply doesn't
exist, and had the same problem after 14 years. The manufacturer
supplied a replacement cartridge at a reasonable price. The only problem
was that the new cartridge felt a lot stiffer than the old one, which
wasn't a serious problem but it was an irritation.

So I'd recommend getting two new cartridges to make sure they both need
the same operating force. Also if one has reached the end of its life,
the other might be getting near. And it saves you having to work out
which one is dripping. :-)

--
Mike Barnes