Water where it is not supposed to be - in general
The pipes, whole drainage system, is such an essential thing nowadays, that we rarely even think about it. Until it breaks of course. Than it is the only thing on our minds - mostly because water isn't the best thing for your furniture and flooring.
It is good to have trusted plumber in times like this, but what if he isn't available? There are some times when you need somebody ASAP, and one man business isn't going to come to your aid. Emergency plumbing services is the answer ? company with more than one plumber, on standby.
All in all, it all comes to trust either way ? You need reliable emergency plumbers. But they all usually have what it takes, to fix your water issues. Besides, it's not like you won't try anyway ? right?
Repairing boiler? Call in the plumber
There are repair jobs, that almost anyone can do themself, but broken boiler isn't one of them. Boiling hot water and immense pressure - those are the things that define boiler, and also the things you should be wary of.
Calling in professional plumber isn't any shame in this case, it is necessesity. It is different from a ticking bomb, but close enough, especially if the safety valves are at fault. All in all, you need expert on this - let him do his job, and relax. He is aware of the risks involved and already knows how to avoid any mistakes. All you need to do is coffee and maybe some snacks, while he do his job.
If you are not convinced by this, and ready to repair you boiler alone, all i have to add is this: search the internet for movies of exploding boilers, I dare you.
Historically about the plumbers by Wikipedia
Wikipedia provides us with brief history of the plumbers:
The word "plumber" dates from the Roman Empire. The Latin for lead is plumbum. Roman roofs used lead in conduits and drain pipes and some were also covered with lead, lead was also used for piping and for making baths. In medieval times anyone who worked with lead was referred to as a plumber as can be seen from an extract of workmen fixing a roof in Westminster Palace and were referred to as plumbers "To Gilbert de Westminster, plumber, working about the roof of the pantry of the little hall, covering it with lead, and about various defects in the roof of the little hall". Thus a person with expertise in working with lead was first known as a Plumbarius which was later shortened to plumber.