All new boilers are condensing – Which means they recycle the warmth within the waste gases – so all 3 forms of boiler will be as effective. The combi offers you hot water on need, but if your boiler breaks you gained’t have any backup (so Commonly the immersion device http://edgarojbum.blogocial.com/How-Much-You-Need-To-Expect-You-ll-Pay-For-A-Good-boiler-installation-31389100