Those licenses that are normally given to plumbers so as to install or work on different gas lines are also the same as the other plumbing licenses that are normally given. There are those states that offer separate certifications to those plumbers who choose to work with propane gas fittings.
Repairing the boiler Never attempt to repair your boiler if it has some issues. Handling electricity can be dangerous and when it is close to water it becomes even more hazardous. When the boiler does not work call on a professional plumber and they will take care of it for you.
Welding the copper lines If there are open torch flames involved in the welding it can be really dangerous. If there are other pipes near there or the wall of the house these can lead to a fire.