Forgot to add, if you can look inside a "heat only" boiler beside a "system boiler" you will immediately see the piping difference's and logic to the layout which helps to put the theory in context.
Old scrappy or removed boilers can let you tinker to your hearts content without worry about damage or if you have some spare bits leftover when you are learning.
Old scrappy or removed boilers can let you tinker to your hearts content without worry about damage or if you have some spare bits leftover when you are learning.