Vent, Valve & Volt
Light switch not working, and the light stays off

This one needs a licensed pro

Likely cause: a three-way switch or its wiring

When two switches share one light and it works from only one of them, or only in certain positions, one of the switches or the wiring between them is at fault. That is a job for a licensed electrician.

Why this happens

This Old House explains that three-way switches let you control one light from two locations, and that one switch losing control of the light after the other is used is a common symptom of three-way switches wired incorrectly. It also describes a frequent mix-up: a single-pole dimmer fitted where a three-way dimmer is needed, so the light works in one switch position only. Sorting it out means opening both switch boxes and testing the wires, and This Old House says a licensed electrician can diagnose these problems quickly.

What to do right now

  1. Try the light from each switch once, first with the other switch up and then with it down. Write down which combinations work. If either switch buzzes, crackles, sparks or feels hot, stop, turn its breaker off and call a licensed electrician.
  2. If the light is dead from every switch in every position, check the panel. Open only the hinged door. Never remove the metal cover behind it; that cover is for electricians. Keep your hands dry and do not stand on a wet floor. If a handle is in the middle or OFF, stand to the side, turn your face away, and push it firmly to OFF, then back to ON. Do this once. If it trips again, leave it off.
  3. Note whether either switch is a dimmer, and whether a switch, a dimmer or the light fixture was changed recently.
  4. Then leave the switches alone and call a licensed electrician. Do not take the cover plates off.

When to stop. Any heat, buzzing, crackling, burning smell or spark at either switch: turn its breaker off and call now.

What to tell the licensed electrician

  • Which switch positions turn the light on and which do not.
  • Whether either switch is a dimmer or smart switch, and its brand.
  • Whether a switch, a dimmer or the fixture was changed before the trouble started.
  • That a bulb you know works made no difference.

Build the full list: what to tell the licensed electrician.

Start this troubleshooter over

References (every fact above comes from one of these pages)
  1. This Old House: How to repair a three-way light switch
  2. This Old House: Why is my dimmer switch not working?
  3. Family Handyman: Light switch not working? Try this.
  4. Family Handyman: How to fix a circuit breaker that keeps tripping
  5. InspectApedia: Electric panel cover removal
  6. ESFI: Flood electrical safety
  7. CPSC Publication 518: home wiring (PDF)

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