Perplexing Electrical Issue

[Ben]

Kinda longish, but I guess you need the backstory.

I have a gas fireplace in the living room. It turns on via an electrical switch. On the same circuit and in the same box are switches for the fireplace blower and an overhead light for the fireplace. I had the propane company out to do a check because the fireplace was randomly turning itself off every 15-60 or so minutes. The tech found some weird voltage drops in the thermopile, so replaced that. Afterwards, though not as often, it still went out.

At this point he figured maybe something was wrong with the electrical switch and suggested replacing it (they can't touch that stuff). So I got a new one and did the replacement. Here is my issue. I am scared of electricity, so I always shut off breakers before I do something like a switch swap. I did so here. However, as I was disconnecting the wires from the old switch (rocker type)  I accidentally flipped the switch. The fireplace came on. I checked the blower and light switches, and they did not come on. So I took my non-contact tester to it. It is "green light safe" red light with beep not safe". The red light came on sorta kinda without a beep.

My thought is there is a low voltage "leak" if that makes sense? Same thing happened after I installed the new switch and tested to see if it would still do it. So is this something with the circuit breaker going bad, or something else? I was reading that some switches are wired to use more than one breaker, but I don't think that's the case here, especially since the blower and light stayed off. I would imagine it must not take a lot of juice to make the fireplace go from pilot to "on".

Anyway, as an electricity idiot, I am confused. On the bright side, the swap did fix the fireplace issue and it has remained on as long as the switch is on.

[Brad Johnson]

Sounds like something is backfeeding the circuit. No unheard of for some enterprising DIYer to use a ground wire as their neutral. I'd have an electrician come in a tone out the circuit just to be safe.

Brad

[Ben]

Sounds like something is backfeeding the circuit. No unheard of for some enterprising DIYer to use a ground wire as their neutral. I'd have an electrician come in a tone out the circuit just to be safe.

Brad

I'm having my electrician buddy come out for other stuff anyway in a couple of weeks and added that to the list. It is something I have never run into before.

[Jim147]

Turn off the pilot. The thermopile will show low voltage as long as it is hot.

[Ben]

Turn off the pilot. The thermopile will show low voltage as long as it is hot.

Ah, so that is where the juice is coming from?

[Jim147]

Possibly. The fireplace doesn't need external power except for the fan.

[Brad Johnson]

I would think the thermopile would be backfeeding voltage at the control board, but not enough to energize the 120V circuit due to angry pixies having to crawl back through the board's power transformer. Are the systems not wired that way?

Brad

[Nick1911]

Ben, sounds like you might have a thermopile, instead of a thermocouple.  These systems generate 750mv (0.75v) from the heat of the fire.  The low voltage goes to your switch, and from there to the main gas valve.  These systems are sensitive to resistance in the circuit.  You probably have worn switch contacts or a connection somewhere in that circuit that is not clean and tight.

[Ben]

Ben, sounds like you might have a thermopile, instead of a thermocouple.  These systems generate 750mv (0.75v) from the heat of the fire.  The low voltage goes to your switch, and from there to the main gas valve.  These systems are sensitive to resistance in the circuit.  You probably have worn switch contacts or a connection somewhere in that circuit that is not clean and tight.

Yes, it's a thermopile. Maybe I should turn off the breaker again and take a multimeter to it instead of the non-contact tester? Though as I mentioned above, with the new switch, everything else seems to be working normally now.

I'll still have my electrician buddy look at it when he comes by.

[K Frame]

As others have said, this isn't a line power from the switch issue, it's a change in resistance over the line issue with the thermopile doing its thing.

The fact that it's going out occasionally could also be a wonky gas valve, or even a loose connection at the gas valve.

The red light coming on on your tester, but without the warning beep, indicates to me that the thermopile is back feeding just enough juice to the line to light the light (which really doesn't take a lot of juice at all).

I've seen dummy testers like the one you describe trigger with a 9 volt radio battery.

[Ben]

The fact that it's going out occasionally could also be a wonky gas valve, or even a loose connection at the gas valve.

The propane guy mentioned that if the switch change didn't help, that he would look at replacing the gas valve. He asked me to call him on his cell (he and his boss  kinda had fun trying to diagnose things) to let me know the outcome. I'll ask him about this and maybe see if he'll just replace the gas valve too and be done with it.

[K Frame]

So you 'lectrocute yourself, or blow up your fireplace yet? 

[Ben]

So you 'lectrocute yourself, or blow up your fireplace yet? 

Not yet, but I broke the tent out for just in case I burn the house down and have to camp. 

I've been turning it on every night and it's working as normal. I'll still have my buddy check it out whenever he makes it out, but it appears to be okay. If the fire was coming on while the switch was off, then I'd be worried.