Strange mixed advice from multiple plumbers
I currently have a vented indirect feed hot water cylinder which is leaking into flats below, I have had several plumbers over to give quotes for replacing it.
However there is an odd variation in the advice being given. One of the plumbers also offered to install a cut-off valve that would prevent the cold water tank feeding the boiler and then the hot water tank, which would allow me to keep the cold water on without water getting into the leaky cylinder. However when I mentioned it to one of the others they said this was dangerous and illegal because the law requires the boiler to be able to feed back into the cold water tank (and have a vent at the other end) to reduce any risk of pressure building up.
Can anyone clarify which is right?