Why Three Way Switch Only Works When One Switch Is On? [7-Step Guide]

If you have a 3-way that will only work when one switch is on; you have come to the right place to get them working properly again! 

In this guide, you will learn:

  • How to troubleshoot a 3-way that only works in one position!
  • Tips for if a three way switch is bad
  • Easy way to identify the wires 
  • And more!
3 way switch only works when one switch is on

Three switches are installed so you can control a light from two different areas of the house.  When you still have to walk across the room because one switch isn't working, it can get very frustrating.  

There are some troubleshooting tips that you can try on your own before having to call in an electrician to have a look at it.  

Keep reading to learn the 7 steps on fixing a 3-way that only works when another switch is on!

Why Does My 3-Way Switch Only Work One Way?

The cause of 3-way not working could be in the wiring, or it could be the switch itself. When working on the wiring, you should not have to do anything with the neutral (white) wires. These wires can just be left tucked in the back of the box. 

A frequent wiring mistake is having the common wire and one of the travelers mixed up. The fix could be as easy as switching the wires around.

If it is a case of the switch being bad, a good practice is just to replace both of them at the same time.  It could be a matter of time and the other one might go bad as well. I also invite you to read my guide on installing 3-way light switches here.

I recommend that before you do any kind of work on three way switches, take a picture of how the wires land on your switch, and to label the wires so they don't get mixed up. This can be easily done with a piece of electrical or masking tape and a marker.

Supplies And Tools Needed

  • Voltage Meter - Used to verify power is off 
  • Screwdriver - Used to make wire terminations, remove and install outlet covers
  • Needle nose Pliers - Used for fixing the hook on the end of the wires
  • Electrical Tape - Used to wrap the outlet around the termination screws as another layer of safety and as marking tape

7-Steps To Fix A 3-Way Switch Where One Switch Has To Be On

  1. Test For A Bad Switch Or Bad Wiring
  2. Turn Power Off and Verify
  3. Label All Wires
  4. Check The Wiring
  5. Turn Power On
  6. Replace Both Switches
  7. Turn Power Back On

Step 1 - Test For A Bad Switch or Bad Wiring 

An easy way to test for a bad switch is just a matter of toggling the switches.

Toggle the switches until the light turns on. 

Toggle switch #1 up and down to see if it will control the light. Leaving the light on, go to switch #2 and toggle that one up and down and see if it will control the light. One of these switches will not control the light and that will be the bad switch. 

Or, if you turn the light on with switch #1, go toggle switch #2 to see if it shuts off. If it shuts off, go back to switch #1 to try and turn it on. If it doesn't turn on, toggle switch #2 again. Go back to switch #1 and the light should now come on.  If this is what you are experiencing, the switches are wired wrong.

Read Also >> How To Wire A Light Fixture With Red, Black, And White Wires?

Step 2 - Turn Power Off and Verify

Go to your breaker panel and turn off the power to the circuit you are working on. Before you start working on the switches, you will want to verify the power is off using your voltage meter.

After removing the cover plate and removing the switch from the box, take one probe and press it to the black screw on the switch. The other probe you will press to the ground screw.  It should read zero volts. Do the same for each wire landed on the brass screws. 

If all read zero volts, it is safe to touch the wires.

3 way switch only works when one switch is on (1)

Step 3 - Label All Wires 

Before removing any wires from the switch, label all the wires according to where they landed and take a picture. If you are replacing the switch, be sure to wire the new switch back up the exact same way. You may want to check out my guide on identifying basic wire colors here.

If there are problems with how the switch is wired, it will be a good reference on where the wires were, so as not to wire it up the same way again.

Step 4 - Check The Wiring

Once the power is off, you can check the wiring. On a 3-way switch, there are 4 terminal screws.  Two are brass colored, one is black, and one is green.  

You want to verify that the black and red wires should be coming from the same cable along with a white and bare copper wire; these are the travelers that land on the brass screws. This needs to be the same on both switches.  

There will be a black coming from a separate cable with only a white and bare copper wire. This should be landed on the black screw, known as the common.  This cable is either coming from a power source or going to the light fixture. 

The bare copper grounds should be pigtailed together, and landed on the green screw.  

The neutral (white) wires should be tied together with a wire nut and tucked into the back of the box.  

All the wires should be folded into the box in a way that once the switch is pushed in, none of the uninsulated sections of wire will be able to touch anything they shouldn't be touching. 

Read Also >> How To Troubleshoot Dead Outlets (And Reset GFCIs)?

Step 5 - Turn Power On

Once you have checked the wiring and tucked the switch back into the box, you can turn the power back on.  

Test your light switches and see if they are working properly.  The best way to test a set of 3-way switches is to toggle each switch to every position to verify the wiring is correct. 

If everything works properly, you are all set! If not, continue on to replace both switches.

Read Also >> How To Wire An Outlet?

Step 6 - Replace Both Switches 

Turn the power back off before you begin replacing both switches.  Making sure your labels are secure, begin removing the wires from each switch.  

Rewire your new switch.  If the hook on the end of the wire opens up when pulling it off the old switch, use your needle nose pliers to curl it back around into a "J" shape.  

Verify that the black common wire coming from the power source or going to the light fixture is terminated on the black screw; the red and black traveler wires are landed on the brass screws, and the bare copper wire is landed on the green screw.  

You should have a set of neutral (white) wires connected together with a wire nut tucked in the back of the box.

This should be the same at both light switches.

Tuck the switches back in the box and put the cover plates back on

Step 7 - Turn Power Back On 

Once everything is buttoned back up, turn the power back on.  Test the switches, like in step 5, to verify everything is working properly!

Read Also >> How To Wire A Light Fixture With Red, Black, And White Wires?

Frequently Asked Questions 

Why Is Only One Of My 3-Way Switches Working?

Only one three way switch could be working because it has been wired incorrectly. The other possibility is that the switch is defective. 

How Do You Troubleshoot A 3-Way Light Switch?

To troubleshoot a 3-way light switch, you will need to check the wires for good connections. Also, verify they are landed on the proper screw. If these all check out, the switch could be defective. 

What Happens If You Wire A Three Way Switch Wrong?

If you wire a three way switch wrong, your lights will only work from one switch.

Is There Always A Hot Wire On A 3-Way Switch?

There is always a hot wire on a three way switch.  It is called the common wire, and lands on the black screw.   

It either is coming from the power source or going to the light fixture. 

What Is The Point of A 3-Way Switch?

The point of a 3-way switch is to control a light fixture from two different locations such as the top and bottom of a staircase. A large dining room, foyer, or bedroom also frequently have three way light switches.

What Is A Three Way Light Switch?

A 3-way switch is used to control lights from 2 separate locations; therefore, you will notice there is no "on" or "off" labeled on the handle of the switch. These switches are also known as single pole double throw or SPDT according to Wikipedia.

Read Also >> What Is The Cost To Replace Knob And Tube Wiring?

Final Thoughts

It can be a little intimidating when it comes to 3-way switches; even more so when they aren't working properly! But if you are comfortable with general electrical wiring, there is no reason you shouldn't be able to do a little troubleshooting on your own to get them fixed! 

Safety is the most important thing, so be sure to double check there is no power on the wires you will be touching! 

If at any point you don't feel comfortable working on the electrical circuit, stop and call your local electrician to come look at what you have going on. It's better to pay that service fee to ensure everything is done safely and properly, than have something go very wrong that could cause a fire or even death.   

I hope you enjoyed this Home Inspector Secrets guide!

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