cars are required to have an MOT by law, to ensure safety. a unit could be installed by a novice and be technically incorrect, so if services were not carried out how would anyone know? i saw a vaillant vantage cylinder connected to a grant boiler on a `Y` PLAN with no 2 port valve, whats the big deal??? yeah yeah,its ok does the job , customer has hot water customer happy!?? looks fine yeah its ok. the point is the system is incorrect because it has NO positive energy cut off, NO over heat protection. so is that ok? no it is`nt really is it. but most DIY`S would`nt` have a clue would they were looking at, so i do thing there comes a point when to much information given to the DIY`er is dangerous, they dont have basic knowlege that a qualified engineer would have, and so will 9 times out of 10 bodge it. anyone think i have a point or am i wrong for thinking DIY`s have there place.