Seems they need to be plumbed into the CH return pipe ?
On my boiler, this is a larger (1" ?) copper pipe which runs through the ceiling into the boiler, and is fixed by wall mounted clips, so it's about 8mm from the wall.
I can't see anyway to lift it off the clips without some straining which I would rather avoid.
Presumably I need to insert a "T" piece into the pipe ... I'm happy to use pre-soldered bits (have done this before elsewhere, with an asbestos mat behind). But is there a way to cut out the necessary section without disturbing the pipe (too much) ?