Like bhg481 I am untrained and have designed and installed my own central heating systems except for the boilers. I don't recall finding the first time difficult or I wouldn't have been inclined to do it again. If you are a practically minded you could certainly change a few rads and alter a bit of pipework I would think. In the last installation I did, I used plastic tubing and expansion connectors, but there is something quite therapeutic about cutting and soldering copper pipes to fit. Have a go, you can always get someone in if you find it isn't for you.