Who says? The so called professional? After years of stripping and servicing my gas boiler I was told by a plumber that I wasnt allowed to do so and he was reporting me. He got nowhere - you might not be allowed to fit your item as a job for someone else but likely you can do what you want to your own boiler. Certainly that applied to me.
Anyway, who is to know. Just get on with it and ignore the BS.
