i have a halstead SBX30 system boiler heating 12 rads and 1 megaflow cylinder in a mains pressure system, the problem is as follows and has been present since install(nearly 4 years ago!!). The pressure shown on the guage on the boiler will drop to nothing, and eventually(over the course of about a week) the boiler produces hideous noises and cuts out. During this 'process' several radiators produce loud bubbling banging noises and fill with air and a large puddle of water is expelled from the system from the drain/overflow outside(copper with open end not plastic one plumbed into waste pipe). The outcome of all this is that the system needs filling(via filling loop) about every week and the rads bleeding. Have had a new expansion vessel fitted(during warranty period) and countless flushes and filling with inhibitor as installer had suggested this as a cause! Have heard these particular boilers are known for probs???? My installer has since 'given up', my wife however hasn't, so any help is greatly appreciated!