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.
Best Answer
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.
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.