Hi everyone. First post on here. Hope I do not need to call on all the experts too many times. Anyhow. Have looked through lots of posts but can not find the definative answer.... I have a baxi 105e INSTANT and the expansion vessel has gone (water out of valve used as a test). Got the part on order, just wanted to know if I can fit it as an external vessel leaving the original one in place (so no need to take boiler off wall and get a corgi engineer in), or do I have to get it done by a professional and fitted inside. Any idea how much the work will cost me if I need it doing professionally?