We have an halstead ace boiler which has started losing pressure intermittently and previously was going over three bar. The only problem we now have is losing pressure. When this happens the boiler will not fire up at all. We have pressured the expansion vessel to 1 bar ish following faq thread. Everything was working fine for two days but the same problem has reoccured. Did notice when hot water was being called for thera was a slight drip from blow off pipe but didnt know whether this was what came from expansion vessel from pressurising. The heating is working ok at min has repressured vessel again but am sure the same will happen again. Would be grateful for any advice.