Drained pint of water from cloakroom rad, reopened valves but did not bleed air. Lasted 1 day but water is still discharging outside. Tonight 22:00 I drained another 1/2 pint without bleeding. Topped up pressure - will see what happens tomorrow.
( I located the expansion vessel about 10 minutes ago (thanks for your advice) . Tomorrow night I 'll do a pressure test and take it from there.
Barry Abel
December 2006