You go to college for 4 years and pass all your exams including your ACS. You must have CCN1 and if you want to work on boilers you must also have CEN1. I personaly have CCN1 CEN1 MET1 HTR1 CKR1 WAT1 CONGLP1LAV CONGLP1PD CONGLP1RHP an HTRLP2. They weren't easy to get and over the years it hasn't been cheap to maintain. We have to be retested every 4 years and it's a pain in the arse. and thats why I can work on someones boiler and you can't.
Sure you could work on your boiler BUT YOU CAN'T DO IT SAFELY!
Just a bit of advise to all you DIYers - leave it alone. It's not just your life at stake!!!!
J, June 2010