You walk into the kitchen after dark, reach for the wall without looking, flip the switch, and the room stays black. You flip it twice more out of habit. A light switch not working is a four-part problem wearing one disguise, because the bulb, the fixture, the switch and the circuit feeding all three produce exactly the same result from the doorway. Sorting out which one failed is mostly a matter of noticing small things: how the switch feels under your finger, whether anything else in the room went dark with it, and what kind of bulb is in the fixture. Everything below can be done without taking a cover plate off, and the article is clear about where an electrician takes over.
Start with the bulb and the fixture, because they fail most
A switch is a simple mechanical part. A bulb is a consumable. When a light stops responding, the odds favor the bulb or the fixture over the switch, so check them first even if it feels too obvious.
With the switch off, try the bulb in a lamp you know works, or put a known-good bulb in the fixture. LED bulbs do not burn out the way incandescents did; they tend to flicker, dim, or die suddenly when the small driver circuit inside them fails, and a dead LED looks perfectly fine. If the fixture has several bulbs and all of them are out at once, the bulb is not the problem.
Then look at the fixture itself. Make sure the bulb is seated; a bulb that has worked loose in a ceiling fixture during a year of door slams is a surprisingly common "switch failure." On a ceiling fan with a light kit, check the pull chain for the light is in the on position, since the wall switch cannot turn on a light the chain has turned off. Older fixtures with a center contact tab in the socket can lose contact when the tab gets pressed flat; if the fixture is a decade or more old and the bulb is good, the socket may be the failure rather than anything on the wall.
What the switch feels like tells you a lot
A healthy toggle switch has a firm, definite click in both directions. Pay attention to the one that stopped working.
If the toggle feels mushy, floppy, or moves without a click, the spring mechanism inside has worn out. Switches are rated for a certain number of cycles, and a kitchen or hallway switch in a busy house gets flipped thousands of times a year. A worn switch sometimes works if you hold it or press it at an angle, which is a sure sign the contacts inside are no longer meeting.
If the toggle is stuck, or moves but with a gritty feel, the mechanism is failing mechanically. Do not force it, and do not spray anything into it.
If the switch plate is warm, discolored around the toggle, or you hear a buzz, crackle or pop when you operate it, stop using it. Heat and noise at a switch mean a loose or arcing connection behind it, and that is one of the ways electrical fires start. Turn off the breaker for that circuit and have it looked at promptly.
A switch with a small built-in light that has gone dark can mean the switch has lost power, which pushes the problem upstream to the circuit rather than the switch.
Dimmers and smart switches fail in their own ways
A dimmer is not a simple switch. It contains electronics, and those electronics are the part that fails. A dimmer that only works at the top of its range, one that flickers LED bulbs, one that buzzes, or one that is warm to the touch is usually either dying or mismatched to the bulbs it controls. Older dimmers built for incandescent loads behave badly with LEDs: flicker, a minimum brightness that is still too bright, bulbs that glow faintly when off, or a refusal to turn on at all. If the problem started when you changed to LED bulbs, the dimmer is almost certainly the issue, and it needs replacing with one rated for LED loads.
Smart switches add a few more possibilities. Most need a neutral wire in the box, and in older homes that wire is not always there, which leads to switches that drop off the network or stop responding. A smart switch that is unresponsive to both the app and its physical button may have lost power or failed; one that responds to the button but not the app has a network problem, not an electrical one. A quick breaker off-and-on reboot fixes a surprising number of them.
Three-way switches make one bad switch look like two
In a hallway, a staircase or a large living room, the same light is controlled from two places. These are three-way switches, and they confuse troubleshooting because the light's state depends on both switches together. When one of them fails, you get a pattern: the light works from one switch only in certain positions, or one switch seems to do nothing at all while the other works sometimes.
Test it by flipping switch A, then switch B, through all four combinations. If the light responds to some combinations and not others, one of the two switches, or the wiring between them, has failed. Three-way switches have more terminals, and the traveler wires between them need to land in the right places; a miswired replacement will produce exactly the symptoms you are trying to fix. Leave three-way replacements to a licensed electrician.
Check whether the whole circuit went dark
If a light switch stopped working and other things in the room are dead too, the switch is probably fine and the circuit is not. Look at nearby outlets with a lamp. Then go to the breaker panel and look for a breaker in the middle position; push it fully off and back on, handling nothing but the switch handle and leaving the panel cover in place. If it trips again, leave it off and call, because a breaker that will not hold is protecting you from a fault, and the post on why a circuit breaker keeps tripping explains what that fault often is.
Bathroom lights are sometimes wired through the bathroom GFCI, and outdoor lights may run through a garage or patio GFCI, so a dead light in those places is worth a press of the Reset button before you blame the switch.
The point where it becomes an electrician's job
Everything above is observation. The next step, taking the plate off and looking at the switch terminals, is not, and the reason is the same one that applies to outlets. The wiring behind a light switch is live unless the breaker is off, switch boxes in older Las Vegas homes can hold more circuits than the one you turned off, and a loose connection you did not notice can arc behind the wall. Three-ways, dimmers and smart switches each have wiring that must be matched correctly.
Call a licensed electrician if the switch is warm, buzzing or discolored; if the breaker will not hold; if a three-way pair misbehaves; if a switch works intermittently; or if you simply do not know what is behind the plate. An electrician will typically find a worn switch, a loose connection on a terminal or a backstabbed wire, a failed dimmer, or occasionally a burned neutral in the box, and will replace the device with one rated for the load on it.
A failed switch is a covered electrical breakdown
Light switches, dimmers and the wiring to them are part of the home's electrical system, and that system is included in every Dwellness plan, starting with the Essential Plan. When a switch wears out, a dimmer fails, or a connection behind the wall goes bad from normal wear and tear, the request goes to Dwellness by web form or by phone at (702) 641-8888, the per-trade service fee is paid at the door, and a licensed local electrician is dispatched. Dwellness has approved 97 percent of claims and has been coordinating repairs like this for Las Vegas homeowners since 1986. Coverage for a home you just bought does not require maintenance records, which is useful when nobody knows what is behind the plates.
Outside the coverage are the things a warranty never pays for: the bulbs, upgrading working switches to dimmers or smart switches, adding switches where there were none, and damage from someone's weekend wiring project. The light switch home warranty page lists what a covered breakdown includes, and the post on whether a home warranty covers electrical covers the wider system, from outlets to the panel.
A dark room usually comes down to a bulb, and the second most likely answer is a tired switch with a worn-out click. Whichever it is, you now know how to tell them apart from the doorway and where the safe stopping point is. For everything behind the plate, a plan that already includes the electrical system means one service request instead of a search for an electrician. Request a free quote at dwellness.house whenever you are ready, or call (702) 509-7007 to talk it through.