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.
Broken boiler vs. 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.
Plumbers and their "toys" - reason we call them
When it comes to professional repairs done by specialists, you often wonder - "ha, I could do that myself, but now I need to pay anyway...". It is common enough way of thinking, but is it really true?
Experts in their fields make it look like it is easy, but only because they have years of experience. Because of it, they were able to deduce what the problem is quickly, and if it is easy to fix, they make it look like it's nothing. It may escape your attention, but they more often than not, use special tools when doing so.
Simple wrench and hammer are common household items, but what about thread seal tape? Or do you really want to buy whole package od putty, just to seal one small hole? These are the things that seperate experts in their fields from weekend handyman. Other than that, they are also the reasons why you call in a real plumber, once in a while.