Installed a new kitchen tap, to replace a 10 year old one where the cold valve had got rather stiff. Perfect - silky smooth ceramic valves in the new tap! But now after just 3-4 weeks, the cold tap has once again got really stiff. I don't understand how this is possible - the water is not very hard, maybe a little but not enough to cause stiffness so quickly, surely? Could there be some debris in the pipework damaging the valve (a 10 year old house)? Any other ideas?