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.

--

Jeff