Jeff Layman wrote in
:

On 27/08/2020 11:37, JohnP wrote:
Slight hiss - took out diaphragm and cleaned it and the seating.
Still passing a bit of water. Anything else worth trying. Could the
float be sticking a bit?
Should I replace it.
Not my house - need to see how accessible the inlet is as I don't
want to remove the cistern.

I had a standard ball float valve which started to overflow a little.
Removing it and cleaning the diaphragm didn't help; in fact, it made
matters worse by starting water hammer. A completely new float valve
was even worse - water hammer and foghorn! Nothing I tried fixed it,
until I turned the pressure down by slightly closing the isolating
valve on the mains input to the float valve. It solved the problem
immediately.

I have a feeling that the water company might have increased the
pressure a little as there was a high demand due to lack of rain, and
that might have contributed to the problem.

Anyway, if there is an isolation valve, it might be worth turning it a
little to restrict the input pressure, and see if that stops the
hissing.


Sorry - turning down a valve reduces max flow - not pressure. Many ball
valves come with a high and a low pressure nozzle or restrictor.