Electrical – Troubleshoot a circuit

It sounds like you have a fixture controlled by a conventional dimmer and are using CFL non-dimmable bulbs.

Standard dimmers were designed for incandescent bulbs. Many CFL and LED bulbs are non-dimmable. Some are dimmable, but only work with special dimmers designed for their electronic circuitry (conventional bulbs have no circuitry, only simple filaments). Some CFL or LED (not many) will work with a standard dimmer.

First you need to make sure the bulbs are dimmable, and then that you have a compatible dimmer.

In general, CFL and LED bulb packages indicate whether they are dimmable or not. If it does not say dimmable, it is probably not. Dimmers also indicate whether they are intended for CFL and/or LED bulbs. Again, if it doesn't mention CFL or LED, it is probably not compatible, unless you have bulbs that specifically say works with standard (or conventional) dimmers.

Check the fixture by using an incandescent bulb. If it works, either go with incandescent, find CFL or LED bulbs that work with standard dimmers or swap out the dimmer.

If the incandescent doesn't work, you have a wiring problem or a defective fixture.

1. Confirm your wall switch is good. Bad switches can be intermittent.
2. Turn off the switch and take the tubes back out and put them back in making sure they're fully snapped in. It's worth a try. Don't go buy more, but if you have other new tubes try them.
3. If the lights work for a period of time and go out on their own, that usually indicates an over-heating ballast - replace the ballast.
4. Otherwise, the best test for a ballast is just what you did, try new tubes. If no luck, replace the ballast.
5. While replacing the ballast, make sure all of the wires in the sockets are well connected. Give them each a little tug. If you can't get a wire to stay in a socket replace the socket, maybe replace all 4.
6. Fluorescent lights need to be grounded to work properly. Make sure a ground wire is attached to the fixture. I've seen fluorescent lights, especially in old homes, where the people say they're always replacing tubes, and it's because the fixture isn't grounded.
7. If you're going to replace the ballast or the entire fixture consider going with an electronic ballast maybe even T8 size tubes. Amazon sells the smaller clips you'd need for a retrofit to T8 U-Bent tubes - ASIN B00A3WGR0W.