Ha ha ha ha ha ha ha ha ha ha ha ha ha
'want to be a plumber'
No, seriously, gas work is fine except is boring as hell, do you seriously want to be servicing/repairing 7-8 boilers 5 days a week? You get asked the same questions in every house and despite working in lots of houses, its a very lonely job.
Plumbing and heating is your bread and butter, its always there to fall back on and you'll always be needed.
I don't care what people say, work for someone else, then its not your problem if work dries up or people dont pay their bill etc. You work 8-5 and thats it, no worrying about if you've got enough work to pay yourself.
Then theres the gas safe certificate and the seperate modules for different appliances, unvented hot water etc etc, the list of courses to be able to fit things is endless, work for yourself and you foot the bill for them, plus loss of earnings. You wont leave college with qualifications to do everything.
Ive been plumbing for 8 years now and i cant say id want to do anything else and i do quite like my job, but i have variety, everything from servicing to bathrooms, rads, full central heating, new builds, Range cookers (Rayburns, Aga's etc) boiler changes, wiring heating systems, we make good everything when we've finished so a bit of brick laying, plastering etc.
As for books, R.D Treloar, Plumbing and gas installations, my bible when i was at college. If you can get a Viper Gas book that'll be a good read for you as well.
Good luck