In ,
Dave scribed:
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?

Dave

Have you checked the pressure of the CH Expansion vessel? (Don't forget to
depressurise the CH first) On my Vaillant, it should be between 0.7 - 0.9
bar. It should have a car-tyre type valve located on it around the base of
the unit which you can check using a car tyre pressure gauge or similar.

Are you seeing any drips coming from the pressure relief valve outlet pipe,
to indicate either that the valve seat is not closing tightly either due to
grit or that the system doesn't have an effective 'shock absorber' because
the expansion vessel has failed?

There is a good FAQ on this he
http://www.makewrite.demon.co.uk/SealedCH.html

hth
Nigel