emergency plumbers London Plumbing in a nutshell - Wikipedia
Wikipedia tells us a little about what plumbing really is:
Plumbing is the system of pipes, drains, fittings, valves, and fixtures installed for the distribution of potable water for drinking, heating and washing, and waterborne waste removal. "Plumbing" also refers to a skilled trade which deals with installation and maintenance.
The plumbing industry is a basic and substantial part of every developed economy. The word derives from the Latin plumbum for lead, as the first effective pipes used in Roman era were lead pipes.
"Plumbing" often denotes the supply and waste system of an individual building, distinguishing it from water supply and sewage systems that serve a group of buildings.
Źródło: https://en.wikipedia.org/wiki/Plumbing
Plumber's snake
A plumber's snake is a slender, flexible auger used to dislodge clogs in plumbing. The plumber's snake is often reserved for difficult clogs that cannot be loosened with a plunger. It is also sometimes called a toilet jack or electric eel.
Plumber's snakes have a coiled (helix-shaped) metal wire with a broader gap between the coils at the terminal end. The operator turns a crank to rotate the helix as it moves through the pipe.
If the clog is caused by a dense, but shreddable obstacle, such as tree roots or glass wool, the auger might break it up enough to enable flow. A small, lightweight obstruction might be snagged or corkscrewed by the auger, enabling the operator to pull it away. As the auger rotates, it also flails against the interior walls of the pipe, scraping off minerals and oil.
Źródło: https://en.wikipedia.org/wiki/Plumber%27s_snake
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.