That was a bit elitist Joe...
Not entirely, to be totally fair to him.
Some one whose skill stops at being able to fling a boiler on the wall, and tie a knot in the gaspipe is a fair bit away from being a heating engineer.
To name a few differences.
ge will be able to tell you in advance what the flow/pressure is at the inlet of a particular boiler connected to a particular pipe.
ge will be able to work out ventilation requirements for old fashioned boilers.
ge will/should be electrically qualified in order to be able to safely and reliably install controls.
ge will have working understanding of electronics in order to be able to diagnose and remedy faults.
ge will be able to calculate/design heat losses/requirements for any building in any location and any conditions to such a degree that the space will warm up fast enough without wasting energy/money and space for installation and gasuse.
Then there is the working knowledge of physics, chemistry and a few other bits and pieces, that set him apart from a boilerfitter, who will know how to screw the parts to the wall and connect them to the pipes safely, but not much more.
