Like I said: your generalisation can't be answered any more accurately than "is an Englishman permitted to drive a car?" or along the analogy of cars: "are cars blue?"
Some are, some are not.
And Likewise I am waiting for you to tell me what zero rated governor equipped boilers are fitted with your vacuum sensing device.
Ben has answered you perfectly; but the sub text you are looking for are the magic words competent; and there is only one way t prove competency.
No "punter" as you put it can change a fan or gas valve on a modern boiler, simply for the fact that they win't have a calibrated FGA or the competency to use it.
Likewise they can not breach the combustion chamber on many modern boilers for the same reason.
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