Expansion vessel pressure query

25 Nov 2007
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United Kingdom
Hello everyone,

Just a quick query regarding expansion vessels as used in a pressurised CH system with combi boiler, in this case, an Ideal Classic Combi FF280.

The 8L vessel should have an initial charge pressure of 0.75 bar.

The system design pressure is 1 bar.

I suspect the expansion vessel may have lost some of its charge, though the diaphragm is definitely not perforated (no water coming out of valve).

Is there any way I can check that the expansion vessel is correctly pressurised without draining down the system? If so, what kind of pressure should I expect if I connect a presure gauge to the "dry" side of the expansion vessel if the "wet" side is at 1 bar or so?

Many thanks.
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No Chris you can't accurately check it with a force on the other side, if it's flat you will almost certainly be increasing your system pressure to well over 3 bar if you try and repressurize without releasing the system pressure. When we say drain down we don't mean a complete drain down, just a release of pressure. If you have time you can do this from a rad bleed....you will just have to keep doing it over and over again as you repressurize the ex. vessel.
Fantastic, Ollski, thanks for the reply. Good to know that I won't have to drain down fully.

At the moment, the pressure seems to be too low when the system's cold, but too high when it's hot. The 3bar safety valve even opened on one occasion. Would this happen if the vessel charge pressure is too low?

I also noticed some funny gurgling noises when the flexible hose that connects the vessel to the boiler was disturbed. Do they sometimes get blocked? Or is this probably nothing to do with the fault?


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