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When we moved in, our natural gas fireplace worked well: Flick the switch & it would ignite.

Years later, it started acting erratically: Sometimes, the switch worked, other times, no luck. We'd try turning the switch off & on again a few times ("Hello, IT. Have you tried turning it off & on again?") and occasionally that would get it going.

Most recently, the workaround hasn't, & the burners fail to ignite 100% of the time. The pilot is fine.

Knowing the fireplace doesn't use the house power (we could use it even during an outage), I figured the voltage was low enough for me to troubleshoot. I disconnected the switch and tried to turn on the fireplace by carefully joining the conductors. This worked 100% of the time. So, I believed the fireplace was OK and decided the switch needed to be replaced.

Since I had it open already, I immediately installed a spare switch I had lying around. This worked well at first, turning the fireplace on & off 100% of the time on that first day. However, the next day, it was acting up again and failing most of the time.

I'm thinking it worked that first day since I'd warmed up the fireplace by connecting the wires, and subsequent attempts that immediately followed, using the new switch, could take advantage of the higher starting heat that generated just enough voltage. However, once the fireplace cooled to the pilot-only ambient temperature the next day, it wasn't enough voltage.

What kind of switch, exactly, should I be getting to fix this? I checked our big-box hardware stores but their switches all seem rated for typical 120V+ use. I spotted thermostats in the fireplace section, yet no switches. Where, generally speaking, might I find what I'm looking for? I'd prefer just a wall switch, and I don't want to call somebody in to fix this.

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Do you have a model number for either the old switch(es) or the fireplace? –  K.A Jan 12 at 21:43
Or pictures of the old switch? –  bib Jan 12 at 22:23
The old switch and the one I tried next are both standard, unremarkable 120V wall switches, the same as anywhere else in my house. I'm guessing the home builder didn't bother with the correct kind of switch for a fireplace though I'm not sure why it would have worked better earlier on. –  Chris W. Rea Jan 12 at 23:50
Just what electricity is being switched? You say that the fireplace doesn't use house power... –  User58220 Jan 13 at 0:02
@User58220 There's a thermocouple in the fireplace capable of generating a small voltage sufficient to control gas flow. I suppose it's possible this piece isn't working as efficiently as before, but I am able to get the fireplace to ignite 100% of the time if I skip the switch and just touch the two leads together. The thermocouple isn't something I can diagnose/fix, so I'm hoping I can address it at the switch. –  Chris W. Rea Jan 13 at 0:18

3 Answers 3

The thermopile in your fireplace puts out millivolts, nothing near the 120V the light switch was designed for. It's probably just a matter of finding a switch with a low enough on resistance. A generic low voltage switch from a electronics store, or ripped out of a toy, would probably do it (for example a 12V SPST). Really here the smaller the better, but beware of anything too cheap as that may put you down the wrong path again.

from discover circuits magazine

There are some fireplace specific forums which could help, particularly with a model number given. An example is http://www.hearth.com/talk/ . The above image is from "Discover Circuits Magazine (December 2009 Issue 4)", which has a guide on this exact topic along with a clever booster solution from one "Mr. Wily Widget". Find it over at http://www.discovercircuits.com/dc-mag/Issue_4/pg-7.htm

You can also try cleaning the thermopile which may have crust of soot. Measure the voltage between those two exposed wires to see if your cleaning makes an improvement.

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I had the same problem, tried everything, replaced the switch and the thermopile, no avail. Then finally I removed the pilot light assembly, the top just pops off and using a straw blew a bunch of dust out of it. The result was a better flame on the thermopile which allowed the valve to open, try that.

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In my previous house I installed an X10 relay to trigger the fireplace from across the room. I never had the switch problem or a problem with the relay.

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Interesting. What might make the X10 relay work well? Might it be designed better for varying voltages, including lower voltages? –  Chris W. Rea Jan 15 at 20:30

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