I am having my existing gas C.H. boiler replaced by a corgie registered fitter soon. My house was built in 1974 and the current gas supply from my gas meter to the current boiler is done in steel pipe, outside diameter approx 25mm. (This goes under a concrete floor at one point.) I note from reading the manual for my new boiler, which I have downloaded, that the gas supply will have to be done to the BS6891 standard. I am confused from reading some things on the net. Can someone tell me if this standard dictates that I will need to have this existing steel pipe replaced by a new (copper?) pipe?