What would you hazard a guess at my CH system volume to be?
Std 3 bed semi, 7 rads of which (1 double, 1 tiny, 1 medium), 15mm pipework
except flow & return between up & downstairs (ie 2 * 2m * 22mm diam).
No cylinder, converting to combi.
It's to determine if the expansion vessel is adequate. 100 litres is the
make or break.

Thanks,
Mike W