Our cold water tank has started overflowing, so this morning, up in the
loft, water off, partially drained cold tank, removed end cap from
valve, removed split pin, wiggled the float arm out and removed the
slider thingy which has a rubber washer in the end. The washer looks to
be extremely worn, but how do I get it out of the slider? More to the
point, how do I get a new one in? Once out, is it just a rubber disc?

Thanks.
--
Graeme