On Fri, 03 Oct 2008 10:49:47 +0100, The Natural Philosopher wrote:

Provided the system is sealed, as in a proper sealed system or a open
vented one with bungs in the feed and expansion pipes then as no air
can get in no water(*) can get out. Just remember to only have *one*
opening at any one time.

And that includes NOT flushing a loo halfway through the job, and having
the cisten ballcock open and let half a tank of scalding hot water over
your wife, who is still upstairs in the other bathroom you left to have
a pee..

I don't get this. The CH circulating water system is totaly isolated from
the distribution of potable water to the places that use it. Surely this
is even the case with these new fangled pressurised combi systems that I
really know naff all about.

--
Cheers
Dave.