AB-07Check the back box for movementIf the socket rocks or the box itself moves in the wall, that's often the real cause of an intermittent fault. How you re-fix it depends on the wall. In solid brick or block, drill out with a 6mm masonry bit and fit new wall plugs with 40mm screws into the box's fixing lugs. In plasterboard on timber studs, drive a 35mm wood screw straight into the timber lug behind the box. In plasterboard on metal studs - common in flats and anything built or refitted since the 1990s - use a self-drilling metal-stud fixing, never a wood screw, which strips straight through 0.5mm steel; work out which you have by running a magnet or stud detector along the wall to trace a line of screw heads, and by checking whether a small pilot hole gives fine timber dust or grey metal swarf. On dot-and-dab plasterboard, use a screw long enough to reach the masonry behind the dab, typically 50-65mm - the plasterboard alone won't hold it. On lath and plaster, screw into the wooden batten behind the laths if there is one, and don't overtighten, as laths crack easily. Before drilling anywhere near a socket, use a cable and pipe detector, but still treat every wall as if something is hidden - detectors miss cables in metal conduit, behind metal-backed board, or run outside the usual safe zones. Keep the circuit isolated at the consumer unit throughout, and if you're at all unsure what's behind the wall, stop and get advice rather than drilling blind.