"NY" wrote in message
o.uk...
"DerbyBorn" wrote in message
2.236...

cistern.

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

+1

Very likely. Could even be overflowing down the back of the cistern if
the
overflow pipe is blocked (presuming it is the type that needs one)

How else would excess water from a dripping ball valve escape if not
through an overflow.

None of mine have ever had an overflow pipe. The overflow ends
up in the pan and all you see is a continual small flow into the pan.

How does the other type of cistern work which doesn't need an overflow?

It ends up in the pan.

Is it possible/legal for the overflow to drain into the normal outflow
from the cistern to the pan?

Certainly possible, but may not be legal there
or maybe the legalitys changed or something.

it is, I'm not sure why all cisterns don't have this sort of overflow.

Yeah, me too, presumably it isnt legal in some places.