Wikipedia about the history of the plumbers
Quick look in to the history of the plumbers, thanks to Wikipedia:
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.
Managing a broken boiler
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.
Plumbing - history
Plumbing originated during ancient civilizations such as the Greek, Roman, Persian, Indian, and Chinese cities as they developed public baths and needed to provide potable water and wastewater removal, for larger numbers of people.6 Standardized earthen plumbing pipes with broad flanges making use of asphalt for preventing leakages appeared in the urban settlements of the Indus Valley Civilization by 2700 B.C.7 The Romans used lead pipe inscriptions to prevent water theft.
Plumbing reached its early apex in ancient Rome, which saw the introduction of expansive systems of aqueducts, tile wastewater removal, and widespread use of lead pipes. With the Fall of Rome both water supply and sanitation stagnated?or regressed?for well over 1,000 years. Improvement was very slow, with little effective progress made until the growth of modern densely populated cities in the 1800s. During this period, public health authorities began pressing for better waste disposal systems to be installed, to prevent or control epidemics of disease. Earlier, the waste disposal system had merely consisted of collecting waste and dumping it on the ground or into a river. Eventually the development of separate, underground water and sewage systems eliminated open sewage ditches and cesspools.