Perishing o ring, lime scale, other debris. Hard to say with no details of
the system.
Brian

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The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"John" wrote in message
2.236...
Recent instal. This morning wife reported only a dribble. Took a look (at
shower) and found that turning it to cold got us a flow (of cold) but
turning it to hot reduced the flow of cold and we got no hot. Suspected a
blockage but there wasn't one.

Any ideas?

Eventually removed the bar - took control valve off end/ Thought some sort
of spool might be sticking so I gave it a good whack onto a bench.

It is now working. - But will it tomorrow??