Before opening either switch box, establish an electrically safe work condition.

Identify the COMMON (black, sometimes labeled COM) terminal on each switch. On a properly wired 3-way, one switch's COMMON is the line feed and the other switch's COMMON is the load (to the light). The remaining two screws on each switch are the travelers.

Painters and DIY swaps frequently re-land wires on the wrong screws. The COMMON screw is a different color from the traveler screws (usually black/dark; travelers are brass).

electrical troubleshooting

Three-way switch not working after paint / re-install

Common symptoms: three way switch; 3-way switch; stair light; switch broken after paint; one switch works other doesn't; switches reversed

Stop and call a pro if:

lockout-tagout-required

Step-by-step diagnostic flow

Step 1
Before opening either switch box, establish an electrically safe work condition.
Step 2
What is the failure mode?
Step 3
Identify the COMMON (black, sometimes labeled COM) terminal on each switch. On a properly wired 3-way, one switch's COMMON is the line feed and the other switch's COMMON is the load (to the light). The remaining two screws on each switch are the travelers.
Painters and DIY swaps frequently re-land wires on the wrong screws. The COMMON screw is a different color from the traveler screws (usually black/dark; travelers are brass).

Possible outcomes

Stop — establish electrically safe condition first

high confidence

NFPA 70E §120.5 — verify zero energy before opening either box.

Safe next steps

Turn off the breaker for this circuit
Verify with a known-good tester at both switch locations

Likely COMMON / traveler swap at one of the switches

high confidence

The single most common failure when a 3-way is re-installed: the line feed or load gets landed on a traveler screw, and one or both switch positions no longer make the circuit.

Safe next steps

With both switches de-energized, identify the COMMON screw on each (different-colored, usually dark)
Land the line-feed black on COMMON at the source-side switch
Land the load (to the light) black on COMMON at the light-side switch
Travelers — the two remaining wires — land on the two brass screws of each switch (either order)
Restore power and test

What to document for a pro

Photos of current wiring at both boxes
How many conductors enter each box

Likely loose connection — high-resistance joint

medium confidence

Flickering/dimming on toggle indicates an intermittent connection, often a backstabbed switch terminal or a wire nut with one strand slipped out.

Safe next steps

De-energize and check every screw terminal for tightness
Re-strip and re-land any backstabbed connections on the side screws instead
Inspect wire nuts in the box — re-twist if any strand is loose

What to document for a pro

Which switch and direction triggers the flicker

Likely traveler-to-common short or wiring error

medium confidence

A light always on / always off can mean two travelers are tied together at one switch, or a traveler is shorting to the common.

Safe next steps

De-energize and visually trace each conductor at both switches
Confirm the line feed and load arrive at COMMON terminals only
If unsure, replace the switch with a labeled, known-good 3-way

What to document for a pro

Photos of both box's wiring
Switch brand

Likely a defective switch

medium confidence

If wiring is verified correct and one switch position consistently fails, the switch contacts may be broken internally — especially after impact, paint contamination, or a fall.

Safe next steps

With power off, swap in a new 3-way switch matching the known-good side

What to document for a pro

Switch brand and approximate age
Whether the switch was painted over

Diagnostic guidance only. If unsure, stop and call a licensed professional — gas, electrical, and refrigerant work is hazardous to untrained users.

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