I know I might not know much about boilers, but I know a little about plumbing :wink: , yes, did close the right one. The 2 big thick pipes on the outsides of the row of pipes. They go from left to right, 1 - CH, 2 - DHW, 3 - Gas, 4 - Cold Water In, 5 - CH, I isolated 1 and 5. 8)