Well, I have to go back to a heating job where the boiler expansion vessel needs changing,. For a number of reasons I intend fitting an external one. I am going to put it below the boiler using a half inch to 15mm adaptor, to 15mm then to a flexible hose to connect to the return to the boiler. Can someone remind me of the max length to the expansion vessel using flex. Yes I am gas safe registered, and yes I am self employed, but no one remembers everything. Kindest regards.