For the past 3 years, my living room recessed lights haven’t worked when the attic is hot. It has gotten progressively worse.

They were installed 20 years ago so I don’t believe it was an installation issue. I have other lights that have wiring in the attic but they are not affected. I spent about 2 hours in the attic looking for loose connections in junction boxes and at each of the 10 lights that are affected. I have even checked the breaker box for loose connections with no luck.

Most recently, I replaced all 3 dimmer switches since I discovered that they can go bad over time. That was a waste since the power to the switches is intermittent. Interestingly, the ceiling fan is on the same circuit and that works even when power to the light switches is interrupted. I hate to call an electrician since this sounds like a fixable issue and I enjoy the challenge. Can anyone help?

  • If you checked for loose connections, a broken wire in insulation might be another possibility, but unlikely if the problem is heat related. It should happen whenever the power has been on for a time, not just in warm/hot weather(power produces heat). I am assuming 20 year old lights are not LED.
    – crip659
    Jun 3, 2023 at 16:19
  • Start at the point closest to the breaker and check from there to the breaker, it could go through another box that has a bad connection. I will take a SWAG and it is connected to a thermostat or something that is turning something on when it gets hot. That thermostat could be not connected to anything else.
    – Gil
    Jun 3, 2023 at 16:22
  • 1
    More diagnostics, less throwing parts at the problem :) Jun 4, 2023 at 1:08
  • 1
    Are these original incandescent lights, or have you replaced them or the bulbs with led ones ? Jun 4, 2023 at 12:57
  • 1
    @crip659 the OP said "recessed lights" that's clearly a term for can lights., Jun 6, 2023 at 13:21

4 Answers 4


Most can lights have a thermal switch that cuts off the power in case of over-heating. They are there if somebody puts a 100 watt bulb when the fixture is rated for only 60 watts (just an example) and it over-heats. The thermal switch cuts power to prevent a fire! Not an issue with LED, but this is a leftover from the days of incandescent bulbs.

In your case, it might be that the attic is getting so hot that the switch cut power thinking it's overheating. If LED, the driver might also have a thermal cutout...not sure.

The fact it's occurring only during the summer and to all the lamps tells me it's almost certainly a thermal cutoff safety switch.

  • 10
    @JohnA Do NOT bypass the safety switches! They are there for a reason. If they are defective, replace them with working switches. Are you sure the switch is defective, and not saving you from a house fire when the light overheats?
    – MackM
    Jun 4, 2023 at 18:21
  • If they are all cutting out at exactly the same time (which we don't know) it's probably not their safety cutouts.
    – jay613
    Jun 6, 2023 at 12:55

Test the thermal switch theory

If ten lights are failing at slightly different times, the thermal switch theory is a good one and you can diagnose that by pulling one of the lights down out of the ceiling and letting it dangle by its cable, or if it is too heavy to make that safe, by hanging it with string or a wire hanger, or disconnecting and replacing it with a simple light bulb pigtail socket. You ought to then see other lights fail but not this one. If that happens you know it's the thermal switches and you can either try to cool the attic, use lower wattage bulbs, or replace the fixtures.

Find the wiring problem

Convenient that the problem is in the attic where you have access to the junction boxes and cables.

If the previous test says "not thermal" (IE the light under test still shuts off even if it's not in the attic or if it's replaced with a simple bulb) or if all the lights are failing at exactly the same time, it's probably not thermal, at least not the thermal switches in the lights. You were already up in the attic and know where the cables are. Make a map of how they are connected and go back to the first junction box that ALL of them have in common, IE the point that feeds them all. Connect a power socket in that junction box, in parallel with the lights, and an extension cord going downstairs. Plug in a lamp and see if that fails when the rest do.

If the new lamp fails in the heat, you know the problem is between the switch and the junction box where it's connected. If it does not, you know the problem is in the wiring from there to the lights, and almost certainly in the piece of cable between there and the next junction box. Move your new power socket from junction box to junction box to narrow down the location of the fault.

You'll find the problem eventually this way.


Dimmer switches themselves have a wattage rating because the triac used for dimming can produce a fair amount of heat. Usually this will be in the range of several hundred watts and is more than enough. But if you do have excessive heat in the environment, this could be a problem. You may want to check the wattage rating on the dimmer switches you have installed and find some with a higher rating. These will typically have large metal fins on the sides to help dissipate heat.

Note that if you install multiple dimmers in a single box, "derating" will often be specified by the manufacturer, which just means that the rated wattage is reduced due to the excess heat produced.

Here's one example on Amazon.

  • I have checked each thermal switch on all 10 recessed incandescent ceiling lights. My multimeter tells me that they are all good. I originally thought one might be defective but after checking it again, I was at fault the first time. I have installed 3 new light switches just for the sake of eliminating that issue. I have power coming to the switches even when the lights will not work. That baffles me. I have power showing at the switches but the only time the lights will work is after sunset. Can some of these thermal switches really be defective but not showing on the multimeter test?
    – John A
    Jun 6, 2023 at 21:22

Since you want to DIY this let's get some tools to do it.

Get a multimeter or non contact tester. Remove the switch and test for power present and switching.

If it is working there then the problem is in the recessed lights. Those cans are fully exposed to the attic heat that can be substantial. You probably have recessed lights can with thermal switch inside. That one could cause problems and the only way to know it to use multimeter to check it.

The fan works regardless since it is not exposed to attic heat.

Making sure (twice) that the power is off on the breaker, reach inside the bulb holder with needle player and pull (bend) the middle contact.

If all of this did not work you need to go to attic (very hot), and inspect the cable run and the connections in the junction boxes.

  • 1
    @GeorgeAnderson could you expand on that please? A source would be ideal.
    – Criggie
    Jun 5, 2023 at 0:43
  • 1
    @Criggie shortly after I answered the OP 's question Ruskies edited his response which looked like text taken from my answer. Jun 5, 2023 at 4:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.