On 17/02/2017 22:40, Rednadnerb wrote:
Graham, Roger, Alan
Thank you but the problem does not occur when the toilet is flushed, only when she is absent from the flat.

OK - how about this. The ball valve doesn't shut off the water
completely when the cistern is at the correct level - and has a slight
drip which slowly raises the level. This is not noticeable when the
toilet is flushed frequently but, if left for a longer time, can reach a
level where it overflows. This would have to be combined with a failure
of the overflow to carry the water away safely - maybe a leak where the
overflow pipe comes out of the side - or bottom - of the cistern.

You could test this by purposely holding the ball-valve down and
overfilling it.
--
Cheers,
Roger
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