Bet his come off a return from a rad which he thought was a flow (Some people think that because it has a TRV on it its going to be a flow, which is not always the case) , and tied what he thought was a return into a return to pick up for his new circuit (If you get the jist) wont work unless the rad his come off is working/trv open etc. I've seen that before with people not knowing what their doing. Its a proper head scratcher when you come up against it as you eyes miss it the first few times because your mind and skill tells you No he wouldnt of done that. My picture I drew up quickly might make it clearer.
