In an earlier contribution to this discussion,
wrote:
hi there
I have a pressure prob with a sealed gfch system.

The pressure shoots up and down - according to the FAQ, this prob
means that the expansion chamber has failed, but when I check the
chamber, there is no water coming out of the valve - only air. Air
pressure is approx 10/11 PSI. I keep topping up water, but there is no
apparent leak...

Any ideas?

Under what conditions did you measure the air pressure? It needs to be done
when the water system is *not* pressurised.

The water is almost certainly being lost through the pressure relief valve,
which opens at 3bar. You need to find where this discharges to the outside
world, and hang a container under the pipe to see how much water you
collect.

As others have said, the problem is probably just that there's insufficient
charge pressure (air) in the expansion vessel. This needs to be pumped up to
about 10 PSI (0.7 bar) when there's no pressure in the water system, and
then you need to use the filling loop to pressurise the water system to
about 1 bar (cold).
--
Cheers,
Roger
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