Ed Sirett wrote:
On Thu, 05 Jan 2006 17:33:17 +0000, Dave wrote:


Nearly a year ago I changed the old vented system to a sealed one,
whilst also adding new rads and splitting it into zones. It all works
well BUT the pressure falls VERY slowly, probably from 1 bar to 0.7 bar
over about 6 weeks.
I can't find any dampness around the rad valves or visible joints so
have resigned myself to waiting for the leak to get worse before I can
find it. Are there any suggestions on how to find the leak, or for
anything I can add to seal the leak (probably not a good idea)?

The GlowWorm book suggests a minimum pressure of 1 bar, is this just to
stop local boiling in the heat exchanger?


Loads of background info in the Sealed CH FAQ.
I doubt the relief valve is dripping but do check.

It will be almost impossible to find a leak that small.
I suggest that you partially drain down and add some internal leak sealer.
(fernox and sentinel do versions), this should seal the tiny leak up.


Thanks Ed, it looks like the bottom line is that it's nothing too much
to worry about; I'll add the sealer next time I need to drain down.

Another question:
When I did the initial design I was worried that the internal expansion
vessel wouldn't be enough for the size of the system (16 rads) so I was
expecting to have to add an additional one. I was expecting to see a
large increase in pressure from cold to hot but I've been surprised at
how little it varies - maybe an increase of 0.2 at the most. Did I just
overestimate the volume of water (and a small pressure increase is
normal) or might there be something else going on?

Dave