In article , Dave
writes
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?

Wot everyone said but also look for stains rather than drips, the leak rate
you describe is very low and will likely evaporate before you see moisture
on a hot system. Fernox and related corrosion inhibitors will leave a brown
stain on evaporation & that is what to look for. I had a similarly slow leak
for a very long time and eventually traced it to a very silly & obvious
position but all I saw was the stain on a pipe, no sign of moisture at all.

HTH
--
fred
Plusnet - I hope you like vanilla