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Old 11-19-2011, 06:56 PM   #1
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Gas Fireplace Pilot Light Won't Stay Lit


Hoping someone can help, my pilot light will not stay lit and the flame seems to touch the thermocouple.

I am going to try and replace the thermocouple and bought a new one that is exact except the connections soldered onto the end that enters the pilot light assembly.

Does anyone know what this is for? Am I going to have to solder something similar onto the replacement part?

Trying to upload a pic unsuccessfully.


Last edited by PugDadda; 11-19-2011 at 06:58 PM. Reason: add pic
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Old 11-19-2011, 07:07 PM   #2
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Gas Fireplace Pilot Light Won't Stay Lit


this looks like some kinda pilot safty .....Why not get oem part from company to be sure....i would not alter a standard thermocoupler...ben

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Old 11-19-2011, 07:14 PM   #3
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Gas Fireplace Pilot Light Won't Stay Lit


Just to confirm. Is the thermocouple that you removed from your fireplace the same as the one in your picture except that it has no spade connections attached to it?

I suspect that this thermocouple is made to be spade connected to a NC limit control. If your old thermocouple did not have this double spade fitting attached to it, you will need to conductively connect these two spades together for the thermocouple to even work. Ohm test the grey end tip of the thermocouple in the picture with its copper casing. You should only have a complete loop when the two spades are pigtailed together.
In a fireplace, these spades and however you connect them will need to be insulated from touching any metal or the gas valve will shut off. Seems like a lot of trouble over just using an ordinary thermocouple.

Last edited by how; 11-19-2011 at 07:19 PM.
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Old 11-19-2011, 07:18 PM   #4
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Gas Fireplace Pilot Light Won't Stay Lit


Quote:
Originally Posted by how View Post
I suspect that this thermocouple is made to be spade connected to a NC limit control. If your old thermocouple did not have this double spade fitting attached to it, you will need to conductively connect these two spades together for the thermostat to even work. Ohm test the grey end tip of the thermocouple that would normally feed into the gas valve with its copper casing. You should only have a complete loop when the two spades are pigtailed together.
In a fireplace, these spades and however you connect them will need to be insulated from touching any metal or the gas valve will shut off. Seems like a lot of trouble over just using an ordinary thermocouple.
Just to be clear. My old thermocouple has this double spade fitting attached to it. The replacement part does NOT. I apologize for not making this clear. I am not even sure what they are designed for?

Just wondering how important they are and if I need them? The manufacturer of the fireplace is Montigo. I would love to buy the original part but cannot locate it!

Thanks for the responses so far...
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Old 11-19-2011, 07:26 PM   #5
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Gas Fireplace Pilot Light Won't Stay Lit


Quote:
Originally Posted by PugDadda View Post
Just to be clear. My old thermocouple has this double spade fitting attached to it. The replacement part does NOT. I apologize for not making this clear. I am not even sure what they are designed for?

Just wondering how important they are and if I need them? The manufacturer of the fireplace is Montigo. I would love to buy the original part but cannot locate it!

Thanks for the responses so far...
did you try www.montigo.com
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Old 11-19-2011, 07:31 PM   #6
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Gas Fireplace Pilot Light Won't Stay Lit


This means that somewhere on your fireplace attached to the leads of your thermocouple is a high limit control. This control is there to shut off the dc current of your thermocouple if the fireplace gets too hot. This will then turn off your gas valve. It functions as a critical safety control and must not be bypassed with a normal thermocouple that has no such connection points or a fire & health danger will be created..

If you have room, you could use a thermocouple test adapter in your gas valve which the normal thermocouple would then fit into. The two spade connections of the test adapter could then be connected to the two wires formally attached to the old thermocoupler. This would bring your safety high limit back into the system to shut everything off if the fireplace got too hot.

Last edited by how; 11-19-2011 at 07:44 PM.
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Old 11-19-2011, 07:45 PM   #7
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Gas Fireplace Pilot Light Won't Stay Lit


I am on the hunt for OEM thermocouple. I used a volt meter and did not get a reading so I assume its the thermocouple. I placed 1 lead at thermocouple and the other lead that enters gas valve... heated thermocouple with a lighter and did not register a reading... Thus, I concluded it was a bad thermocouple.

If I cannot find OEM part, should I attempt to solder on a spade connector?
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Old 11-19-2011, 07:59 PM   #8
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Gas Fireplace Pilot Light Won't Stay Lit


The dc current can only be measured on that thermocouple between the grey tip (in the picture)and the copper of the thermocoupler line and only when those two thermocouple spade terminals are connected to each other. I would only do that with the thermocoupler in place in the fireplace pilot assembly so that I'd be testing it with natural gas and within the only fireplace pilot flame normally available for the thermocouple.
After that test (if the thermocoupler seemed OK) I'd do it again with the original limit control wires back in place on that thermocoupler.


A tripped high limit/ poor connections/ worn wires could well be the reason your pilot stoped working.

Last edited by how; 11-19-2011 at 08:05 PM.
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Old 11-19-2011, 08:25 PM   #9
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Gas Fireplace Pilot Light Won't Stay Lit


Would sanding the thermocouple tip be a potential fix?
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Old 11-19-2011, 09:05 PM   #10
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Gas Fireplace Pilot Light Won't Stay Lit


No it wouldn't. I think Post 8 is the next logical diagnostic step.
A thermocouple produces the dc current through the difference in temp between the hot junction(its tip) and the cold junction 2.5 " away from the tip. The potential difference in that dc currant is created and carried by the exterier copper thermocouple covering and an insulated line inside of it.
In your system those spade terminals feed that dc current out from the inner wire to the limit control and back again to complete the loop through to the gas valve. Unless those two spade connections are conductively connected then the continuity is broken and you won't get any measurement out of the old thermocouple.

Last edited by how; 11-19-2011 at 09:24 PM.
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Old 11-19-2011, 09:55 PM   #11
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Gas Fireplace Pilot Light Won't Stay Lit


I was able to get a reading with OHMS but nothing for volts.

Can you outline steps to measure voltage?

1. Heat thermocouple
2. Place one lead on thermocouple
3. Place 2nd lead where? I have been putting it on copper section close to where it goes into pilot assembly

I wish I would have paid more attention in physics!
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Old 11-19-2011, 11:01 PM   #12
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Gas Fireplace Pilot Light Won't Stay Lit


Set your meter to dc milli Voltage. One lead of the meter should be attached to the very end of the thermocoupler that normally goes into the gas valve.(the end that is shown in your picture). The other meter lead should be attached to the copper exterier of the thin thermocoupler line.

Attach a short piece of wire to two spade connecters and put them on the thermocoupler spade connections shown in your picture. You want the two spade connections on the thermocoupler joined to each other. Alligater clips connected together by a short length of wire will also work.

Heat the tip of the thermocoupler and read what the meter says.

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