Limescale in the pipe blocking it from time to time.
Brian

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This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Rednadnerb" wrote in message
...
Update:

I gave up with this after emptying a full bath produced no results.

Some months later her neighbour had a pinhole leak in a mains pressure
copper pipe under the floor, fortunately it was above a car drive through
so no damage downstairs.

When this leak was fixed her problem disappeared.

The damaged pipe was close to the area of the mystery puddle, maybe a
couple of meters and at a slightly higher level.

Too much of a coincidence not to be connected.

All that remains unexplained is why the leak was intermittent but I think
the case is closed.

Thank you all for your help.