I am going to replace my exsisting 30 year old 'glow worm' gas central heating boiler.i am of course going to replace it with a 'condensing' boiler which will be a 'conventional' type on my vented system.My problem is that the original boiler has 4 pipes(not including the gas), to it and the new ones all appear to have just three, one of which is the gas( the one ill get a corgi fitter to join up!).Has anyone any idea how to do the job, without the obvious answer, get a pro to do it!!!