@jerzone oh it’s the potable water, going from the core in the boiler to the mixing valve.

a copper elbow sprung a leak (metal thin with minerals and time) i cut off 2 elbows and replaced a section with sharkbite fittings. three months later one of the sharkbites started leaking.

i think the problem is that piece of copper is slightly out-of-round, the walls of the pipe are very thin. i’ll clean it all up and reassemble, hope it holds until i can get someone here to sweat new copper fittings.