On Tue, 19 Oct 2004 10:47:24 +0100, "Christian McArdle"
wrote:

The pressure relief valve however, has expelled more water and now the
system is down to 0.8 bar according to the guage. (It was 2.0 bar when
I toppd up the pressure just 5 hours ago).

How much does the pressure rise when between cold and hot? If the pressure
rise is 1 bar, then the expansion vessel is either shot or undersized. It
is better to calculate a system that only gives = 0.5 bar rise and
pressurise to 1 bar when cold. With 3 storeys, the design should be more
specific and will depend on the relative vertical locations of the
components.

I suspect that if you have a system that rises 1 bar and starts at 2 bar
cold, then it will be activating the pressure relief, which may depressurise
the system considerably. The fix is to repair/add an additional vessel (if
required) and set to 1 bar cold.

Funnily enough, the system seems to be working fine since I finished
the work on it yeaterday, depite the odd symptoms I mentioned:
(pressure valve blowing at 2-bar instead or 3-bar, according to the
guage). When cold, the system, reads around 1 bar on the guage and
rises to about 2 bar when hot. Does that sound about right? (it's a
smallish 3-bed house) The technical help guy at the boiler's main
office, told me the system can typically rise as much as 1.5 bar as it
gets hotter. No more water has been expelled from the pressure guage
since yesterday.

The only symptom that really puzzles me is that the 3-bar
pressure-relief valve blows at 2 bar instead of 3-bar. So did the old
one I replaced. So I suspect that the pressure guage is giving an
incorrect reading. I'm not sure how long it's ben doing that for.

I guess there is no real danger, since the pressure relief valve blows
at somwhere between 2 and 3 bar. Would you agree?


Cheers,

Dave L