Had BG man here this am to service boiler. Before he left I asked him to check a radiator which seemed to have had a slow but persistent leak. He tightened up the joints and left, saying we weren't covered for radiators on our policy but if that had not worked they could replace it for a one-off fee . Put heating on , turned the TRV down a bit as it was on max a little later heard a noise and it has now broken off. Is replacing the TRV control straightforward ?