The beginings of plumbing
Plumbing was very rare until modern cities grew in the 19th century. At about the same time, public health leaders began wanting better systems to get rid of waste. Before this, people got rid of waste by collecting it and dumping it onto the ground or into rivers. However, there were some plumbing pipes in the city settlements of the Indus Valley Civilization by 2700 B.C. Plumbing was also used during the ancient civilizations such as the Greek, Roman, Persian, Indian, and Chinese civilizations as they built public baths and needed drinking water, and somewhere to drain waste. The Romans used pipe inscriptions to stop people from stealing water.
These systems did not improve much over the years. There were almost no improvements from the time of the Roman aqueducts and lead pipes until the 19th century. Eventually the development of separate, underground water and sewage systems got rid of open sewage ditches and cesspools. Most large cities today send solid wastes through pipes to sewage treatment plants. Treatment separates water from waste and makes the water more pure before it goes into streams or other bodies of water. Most places stopped using lead for drinking water after World War II because of the dangers of lead poisoning. At this time, copper piping was started because it was safer than using lead pipes.
Historically about the plumbers by Wikipedia
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.