Project Guide

How to Fix Christmas Lights

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Identify the Problem
Woman hangs an ornament on a lit and decorated Christmas tree.

Your holiday lights may have gone out for any of the following reasons:

  • The circuit isn’t carrying power.
  • A fuse has blown.
  • The wire has broken.
  • One or more bulbs are not seated properly in their sockets.
  • A bulb has burnt out and its shunt is not passing on electricity.
  • A bulb has burnt out and has created a cascading outage.

The following steps will address how to check for and solve all of these potential problems.

Test the Circuit
A hand holds a circuit tester inserted into a wall outlet.
  • Make sure the strand is properly plugged in.
  • Test the outlet with a strand that you know works.
  • If the outlet is working, move on to step 3.
  • If the outlet is not working, check the main service panel and make sure that the circuit breaker is ON and has not tripped.
  • Test the outlet with a circuit tester to ensure it is carrying power properly. If not, use a different outlet for your lights and call an experienced electrician to fix the nonfunctioning outlet.
  • If you are using battery operated Christmas lights, skip the above steps and start by changing the batteries.
Check the Fuse
A plug fuse compartment is opened to reveal two glass fuses, while two replacement fuses sit nearby.
  • Holiday lights usually have cartridge fuses in a small compartment in the cord plug behind a sliding door. Learning how to change a fuse in Christmas lights is simple, but if your strand of lights does not appear to have accessible fuses, move on to step 4.
  • Open the sliding compartment door and remove the fuse(s). The fuse is a small, glass cylinder with metal-plated ends and an internal metal filament. You can sometimes tell by sight if a fuse has blown; the metal filament inside the glass cylinder will have a break in it. 
  • Replace the blown fuse with a replacement fuse of identical size and rating.
  • If you can’t tell by sight that a fuse is broken, test each fuse by replacing it with a fuse you know is working from a functioning light strand. 
  • If all the fuses are functioning, move on to step 4.
Check the Strand
Woman holds up a strand of multicolored Christmas lights next to an undecorated Christmas tree.
  • Completely unravel your string lights and check for broken wires and sockets. Keep in mind that all the “wires” on the strand may not actually be electrical wires—some are there for aesthetic or support reasons and are not a part of the circuit panel. If there are broken parts of the strand that do not appear to have any electrical wires inside, then they are likely not affecting the lights.
  • If a broken strand does have electrical wires poking through, then discard the strand. Reserve the bulbs to use as replacements for other strands of Christmas lights.
  • If the strand appears fine, move on to inspecting the individual sockets and bulbs. 
Check Each Bulb
Two hands screw a replacement light bulb into a socket on a strand of string lights.
  • Ensure each bulb is seated properly and fully in its socket. 
  • Bulbs that have burned out should be easily detectible, since the glass will be darkened around the broken filament. Unplug the strand and replace the bad bulb with a new bulb of the same size and the same voltage rating. String lights usually come with extra bulbs, but you can also purchase replacement Christmas light bulbs of all voltage ratings, including replacement C9 Christmas light bulbs and replacement C7 Christmas light bulbs. You can also find both colored and clear replacement Christmas light bulbs.
  • Thanks to a backup filament known as the “shunt,” burnt-out bulbs will not disrupt the flow of electricity to the rest of the strand. If the rest of the strand does appear affected by the burnt-out bulb, the shunt is also nonfunctioning. Replace the bad bulb as you would normally.  
  • If you cannot detect any burnt-out bulbs or a large chunk of lights are still not functioning, move on to step 5.
Test the Bulbs
A LightKeeper Pro light tester tests one of the light bulbs on a strand of Christmas tree lights.
  • Use a light tester to test each bulb individually. Sometimes nonfunctioning Christmas light bulbs can appear to be perfectly normal, so a light tester is the most efficient and reliable way to single out broken bulbs. 
  • Replace all nonfunctioning bulbs.
  • You can also test the bulbs without a light tester, although this process will take more time. First find a socket that you know works and mark it with a piece of tape. Next, remove all the bulbs from the nonfunctioning section of the strand. Put them in a bowl for untested bulbs. Use a separate bowl for tested and working bulbs. Plug in the strand and start testing each bulb by putting it in the indicated socket. If it lights up, you know the bulb works, and you can place it in the working bulbs bowl. Discard any bulbs that do not light up. Continue this process until you have tested every bulb. Put the working bulbs back in the sockets and replace the nonfunctioning bulbs you discarded. 
General Troubleshooting
Man contemplates a single unlit bulb on a strand of Christmas tree lights.

If you follow the above steps, you should know how to fix Christmas tree lights, icicle lights, LED Christmas lights and any other type of string light. Here are a few more general tips to keep in mind when troubleshooting Christmas lights:

  • Buying Christmas light replacement bulbs should always be your last step. Modern string lights have shunts to redirect the flow of electricity when a bulb burns out, so only the individual light bulb is affected. When an entire panel of lights is out, the reason is almost never a single burnt-out bulb, unless that bulb’s shunt is also broken. To save yourself time, prioritize checking the fuse and strand before replacing bulbs. 
  • While they prevent a single bulb from disrupting an entire panel of bulbs, shunts also give rise to a new problem: cascading outages. When a single bulb goes out, the shunt passes along the electricity to the next bulb. The subsequent bulbs on the strand take on the additional amount of electricity that was supposed to go to the burnt-out bulb. This puts each bulb under slightly more strain, making them burn brighter until they eventually burn out as well, leaving you wondering how to fix Christmas lights that are half out. The only way to correct this problem is to replace burnt-out bulbs quickly to prevent the cascading outage. If a major outage has already happened, you must replace the first burnt-out bulb and every bulb that follows it.
  • When determining how to fix Christmas tree lights on a pre-lit Christmas tree, keep in mind that larger trees will have two to three strands, and the main plug may not be at the lowest section of the tree. Usually the main problem is that one of the plugs has become partially or fully disconnected.
  • The typical holiday light strand lasts between 1,000 and 1,500 hours, which translates to approximately two to three holiday seasons. Some strands may have simply reached the end of their lifespan. LED Christmas lights have a considerably longer life, usually lasting up to ten times longer than traditional lights.
How to Care for Your Christmas Lights
A woman carefully removes a strand of Christmas lights from a decorated tree.

Christmas lights are fragile, so correctly caring for them during and between holiday seasons is essential to keep them functioning.

Holiday season care:

  • Turn off and disconnect plug-in Christmas lights when not in use and before going to sleep at night.
  • Hang ornaments from the branches of your tree. Never hang them from the light strand.
  • Keep natural trees well-watered because dry branches and needles are significantly more flammable.

After-season storage:

  • Take down the Christmas lights carefully, without pulling on or twisting them. 
  • Plug the light strands in before storing them, to ensure they are still functioning.
  • Replace malfunctioning bulbs and fuses so that the lights are ready for next season.
  • Coil the strand loosely and secure it with twist ties, so that it does not tangle with other strands in storage.
  • Place the strands in their original packaging or a similar container and store them in a dry, safe area away from children and pets.

Now that you know how to fix them, your Christmas tree lights should keep shining brightly for years to come. Shop our selection of Christmas lights and replacement bulbs today. The Home Depot delivers online orders when and where you need them.