Boiler manual and y pics?

My son is in the boiler servicing game, and he has a van crammed with all sorts of computerized gear for testing boilers, something like �3000 of testing gear, I remember him telling me of people who studied manuals of their boilers, and attempted to fix their own. sadly they had to admit defeat , and bring in the experts, in one scenario the householder went and bought an expensive panel at top price, fitted it, and it burnt out in front of his eyes.