jim k wrote:

DerbyBorn Wrote in message:
The cistern must be at overflowing level. A bit of a fluctuation in th
epressure is allowing the ball valve to pass a bit of water that is then
causing an overflow into the bowl - assuming it is an inegral overflow.

Try reducing the water level to about !cm below the overflow.


Worth a look but I can't think why that doesn't happen when sink
or bath taps operated?

Of course it shouldn't happen at all on dropping the pressure if the
ball valve is working properly. My theory is that some imperfection or
dirt on the seating allows it to leak when the pressure falls just below
the resting mains pressure (presumably regulated at the stree stopcock)
allowing part of the diaphragm to lift slightly. But when the pressure
falls further the shape changes further and it seals again at another
part of the diaphragm radius.. If this is true, there will be a rate of
carefully adjusted flow from the tap which will duplicate the effect of
the shower.
So, a testable hypothesis!

--

Roger Hayter