Hi, I'm hoping to get a bit of advice on some plastic stop ends I have installed in my flat. One in particular is used to cap off a pipe that used to supply the flat's hot water cyclinder from a communal water tank in the roof. The cylinder has now been removed hence the stop end. I don't have easy access to a shut off tap for this supply but I assume there is one in the locked roof space. While fitting some shelving near to the cap I knocked it and a drop of water appeared a little while later. Since then there has been no more leak. Should I be worried about these stop caps or are they generally reliable? Thanks in advance...