Replace a light switch like-for-like

Turn off the power safely, swap over the wires, and fit a matching new light switch in one session.

LS-01Buy a matching switch and gather toolsMatch the new switch exactly to the old one: same number of gangs, same type (1-way or 2-way/intermediate if it's a stairs light), and a plate size that covers the existing hole. Get a flat and cross-head screwdriver, a torch, and your voltage tester. Take a clear photo of the old switch and its wiring before you touch anything, so you have something to check against later.

RULES

1 each · Replacement light switch (matching gang/type)

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KNOW THE RULES

Like-for-like switch replacement is not notifiable under Part P. But if the switch is in a bathroom or shower room, UK wiring rules (BS 7671) only allow certain types there, such as a pull-cord switch or one sited outside the room - check this before you buy.

LS-02Turn off the power and prove it's deadSwitch off the lighting circuit at the consumer unit - it's usually labelled 'lights' or similar. If you're not sure which MCB it is, turn off the whole consumer unit instead. Use your voltage tester on the switch terminals to prove there's no power before you go any further.

LS-03Remove the old faceplateUndo the two fixing screws holding the faceplate to the mounting box and pull it away gently. Note or photograph which wire sits in which terminal - most switches have just 2 or 3 wires, plus a strap wire on 2-way switches. Loosen each terminal screw and free the wires.

LS-04Check whether the mounting box needs re-fixingIf the box is still firm against the wall, leave it and move to wiring the new switch. If it's loose or the screw holes have worn away, you'll need to work out what's behind the wall before drilling: run a stud detector or magnet along the wall for a line of screw heads, listen for a hollow sound between studs versus solid on a stud, and drill a small pilot hole - timber dust means a timber stud, fine steel swarf means a metal stud, and no dust with a hollow sound means plasterboard between studs. Metal studs are common in flats and anything built or refitted since the 1990s.

LS-05Drill and re-fix the box, if neededCables and pipes can run almost anywhere, and a metal stud frame can confuse cheap detectors further, so use a detector but still assume something's there until you've proved otherwise. Before you drill, find your stopcock (usually under the kitchen sink) and check it turns, so you can shut off the water fast if you hit a pipe - and make sure the lighting circuit is still off at the consumer unit. For a timber stud, use a 3.5x30mm wood screw straight into its centre; for a metal stud, use a self-drilling metal-stud screw, never a wood screw or wall plug, which strips straight through 0.5mm steel. In solid brick or block, drill a 6mm hole 35mm deep and use a red wall plug with a 3.5x30mm screw; for dot-and-dab, use a fixing long enough to pass through the plasterboard and bite at least 25mm into the masonry behind (usually 50-60mm total); for lath and plaster, use a plasterboard toggle fixing rated for the box's weight rather than screwing into the crumbly lath.

1 pack · Red wall plugs (6mm) pack

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4 each · 3.5x30mm screws

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4 each · Self-drilling metal-stud screws

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2 each · Plasterboard toggle fixings

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LS-06Wire the new switchUsing your photo, connect each wire to the matching terminal on the new switch - usually the same red/brown live wires and any strap wire for a 2-way switch. Tighten each terminal screw firmly and give each wire a gentle tug to check it's held. Make sure no bare copper is visible outside the terminal.

LS-07Fix the new faceplate to the boxTuck the wires neatly into the box so the plate sits flat against the wall. Screw the faceplate on using the screws supplied with it, tightening evenly on both sides. Don't overtighten - plastic plates crack easily, and the plate should sit flush and level.

LS-08Restore the power and testSwitch the lighting circuit back on at the consumer unit and try the new switch. Check the light works properly from every position if it's a 2-way switch. Feel the faceplate after a few minutes - warmth or buzzing means a loose connection, so turn off and recheck the terminals.

LS-09Tidy upWipe any dust or plaster off the wall and skirting below. Put the old switch aside for electrical recycling rather than the general bin. Put your tools away and store any leftover fixings for next time.

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