I have discovered an inspection hatch in the back wall of my house. I think it is aluminium approx 25cm x 20cm. It is frame with an inset panel, which if you remove the two screws reveals the cavity and the drain points for the radiators. It is broken and I need to a new one but I have no idea what it would be called. Any pointers appreciated.....so I can get replacing it. Thanks for any help.