Materials used in plumbing
Water systems in ancient times used gravity to move water. They used pipes or channels usually made of clay, lead, bamboo or stone. Today, water-supply systems use a network of high-pressure pumps, and pipes are now made of copper, brass, plastic, or other nontoxic material. Drain and vent lines are made of plastic, steel, cast-iron, and lead. Lead is not used in pipes today because it can be poisonous.
The 'straight' sections of plumbing systems are of pipe or tube. A pipe is usually made by casting or welding, where a tube is made through extrusion. Pipe usually has thicker walls and may be threaded or welded, where tubes have thinner walls, and needs special joining techniques such as 'brazing', 'compression fitting', 'crimping', or for plastics, 'solvent welding'.
As well as the straight pipe or tubing, many fittings are required in plumbing systems, such as valves, elbows, tees, and unions.
Plumbing fixtures are designed for the people who use the water. Some examples of fixtures include water closets (also known as toilets), urinals, bidets, showers, bathtubs, utility and kitchen sinks, drinking fountains, ice makers, humidifiers, air washers, fountains, and eye wash stations.
History of the plumbers - 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.
Boiler repair - call in the specialist
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.