# Gas fireplace burns, then shuts down



## mmvillar (Dec 4, 2011)

I have a Majestic direct vent gas fireplace. Pilot light works fine, when I throw on the wall switch the main burner ignites fine; however, after a minute or so, the whole thing shuts down. The pilot will re-light without problem and the whole sequence can be repeated ad infinitum. There is a perceptible "click" when the unit shuts down (i.e. the gas stops flowing). Gas repairman replaced the thermocoupler saying that it was a guessing game as to what was wrong. That didn't help. He now says the only other thing it can be is the valve assembly itself. Before I make that investment, I'd like to hear the thoughts of others on this.
To add to the mystery, the burner stayed lit for several hours a couple of days in a row. I actually had to turn it off. But now, its back to the same routine. Any suggestions are appreciated.


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## hvactech126 (Nov 11, 2010)

check the exhaust and intake they may be partially plugged. Make sure the flame is engulfing the t-couple the whole time during the burn. The pilot may just need cleaned.


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## biggles (Jan 1, 2008)

remove the stat off the subbase jump R to W if it gives you a steady run ....remove the jumper then go down to the furnace and jump the R to W should get the same constant run till you pull the jump..if you get a shutdown with the furnace juming then something inside is knocking the gas out..get back with yes or no's...note on jumping you are acting like the thermostat by having it on or off....it's just a control circuit closure like a light switch:wink: nothing is going to heat unless R and W connect or are rubbing on each other away from the stat..anybody nail into the wall lately


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## hvactech126 (Nov 11, 2010)

biggles said:


> remove the stat off the subbase jump R to W if it gives you a steady run ....remove the jumper then go down to the furnace and jump the R to W should get the same constant run till you pull the jump..if you get a shutdown with the furnace juming then something inside is knocking the gas out..get back with yes or no's...note on jumping you are acting like the thermostat by having it on or off....it's just a control circuit closure like a light switch:wink: nothing is going to heat unless R and W connect or are rubbing on each other away from the stat..anybody nail into the wall lately


maybe you missed that it is a direct vent FIREPLACE and uses a WALL SWITCH!!!!!!!!


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## biggles (Jan 1, 2008)

sorry about that ....:huh:WEAK transformer.....:wink:


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## mmvillar (Dec 4, 2011)

*Fireplace problem*

Thanks, guys, I'll try those things. Gas tech guy who came out said there was no transformer. Is the only electricity in this thing generated by the heat?


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## how (Feb 26, 2011)

I think have a milli volt powerpile driven fireplace. That means that only 1/2 of a volt powers the gas valve, the wall switch, the wiring and a high limit button. Any wiring connections that are not perfectly tight will cause problems. Check every connection you can find.
Do you have both a thermopile 1/2" thick *and* a thermocoupler 1/8" thick in the pilot flame? 
The flame has to envelope the power pile/ thermocoupler during the entire heating cycle and any draft that pulls the pilot flame away from either will cause the gas valve to lock out. 
A picture of the pilot assy would help.


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## mmvillar (Dec 4, 2011)

*Gas fireplace shut down update*

Following suggestions, I've cleaned the pilot orifice and made sure all elect connections are tight. I tried to attach a photo of the pilot assembly while lit but the size exceeded the website limit. (I'll try to fix that)
The thermopile/generator (the thing in the foreground) was replaced by the gas mechanic. The pilot flame engulfs the thermocoupler and makes full contact with the tpile but I can't say it engulfs it. I tried turning what looked like an adjustment screw labeled "pilot" but the flame didn't go up or down. Again, the pilot light will burn forever and the burner never fails to ignite and burn for a time; however, within a couple of minutes it clicks and everything shuts down. Thanks for your help.


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## how (Feb 26, 2011)

I would try bypassing the wall switch at the gas valve with a pigtail ( a wire with allligator clips at both ends). Can you identify the two wall switch wires that are connected to your gas valve? 

A picture or the gas valve & pilot assemble really would help.


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## mmvillar (Dec 4, 2011)

*More info, problem still exists*

I'm back!
I have replaced the whole valve assembly and my repairman has replaced the thermopile twice! Things worked okay for 20 mins, the repairman left and the whole thing shut down (burner and pilot). I put a voltmeter on the thermopile leads and discovered that the voltage stays stable with the pilot on- and no burner. But, when I switch on the burner, it lights and the thermopile voltage then starts dropping- very slowly- but then it hits a threshold and shuts the system down.
I can re-light the pilot, the voltage builds up but when I light the burner, the voltage drops, system shuts down, etc etc.
I'm afraid the electrical component of this problem is over my repairman's head....and also over mine. Any ideas on why this is happening?


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## mmvillar (Dec 4, 2011)

*Also*

btw, I did bypass the wall switch with a pigtail but that was no solution.


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## how (Feb 26, 2011)

Can you see the pilot flame around the thermopile when the main burner comes on. Move a log to make it visable if you have to. Is that pilot flame getting smaller, becoming softer, more yellow with the burner on when that dcmv output starts dropping?
and..
How many wires are connected to your gas valve?


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## oldguy2 (Jan 14, 2009)

fireplace vent needs to have a restricter plate inserted in the venting to keep flames from lifting off the pilot assembly. restrictor plate is a round disk with a 3 inch hole in the center of it.


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## mmvillar (Dec 4, 2011)

*followup*

Here's more info based on your inputs:
I cannot see any change in the flame that hits the thermopile when the burner kicks on and I can't see a change just before everything shuts down. Like I said before, I do see a slow voltage drop from the thermopile to the point where it shuts down. While the pilot flame looks "healthy" to me, I'm not a gas repair guy. The flame hits the thermopile and sort of bends upward vertically. It stays in contact with the tp but is only hitting one side. That apparently is sufficient to get the voltage up to where the valve will open, but then something I cannot see happens. (Again, this is the second new tp put in). Also, there are 2 pairs of wires going to the valve. One pair from the thermopile and one pair from an on/off switch.
(i.e. there is no overheat sensor or anything like that)

Regarding the venting. This is a direct vent to a 4 inch vent pipe, up through the roof. Does this restrictor you mention close it down to a 3 inch pipe? I presume this is to cut down on the "draft" and keep the flame more stable?? Once again, while the flames lick and move, they don't appear to be blowing excessively and they are not lifting off the pilot.
I appreciate you guys giving me your ideas. I'm fresh out.


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## oldguy2 (Jan 14, 2009)

you just gave yourself the answer to your problem.the flame turns toward thermocouple and then goes vertically.that restricter plate will slow down your draft. keeping the flame on the thermocouple.its a 10 dollar part.


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## oldguy2 (Jan 14, 2009)

the restricter plate for majestic is a round collar with a piece of metal in the center of it.spliting the 4" into two halfs. in the install instructions it clearly says when venting vertically to install restricter plate.


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## mmvillar (Dec 4, 2011)

*Makes sense*

that makes sense. Any idea where I get a restrictor plate? And, does it mount at the mouth of the vent, just as it leaves the firebox?
To be clear, I'd be reducing the vent opening from 4 inches to 3, correct?


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## willijv (Feb 6, 2011)

*Fire Place shutting down*

I missed whether you were on propane or natural gas. I had the same problem with my unit on propane. Found out I was getting ice crystals at the regulator and gas pressure was dropping off. As soon as the unit would go off, it was enough time for the crystals to melt and it would light back again and run for awhile. Propane supplier put some alcohol in the tank and problem went away.


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## Carlton (Jan 3, 2012)

*Same problem (Fixed)!!*



hvactech126 said:


> check the exhaust and intake they may be partially plugged. Make sure the flame is engulfing the t-couple the whole time during the burn. The pilot may just need cleaned.


 I had the exact same problem for a couple of days.I don exactly what havctech 126 sajd.I cleaned the pilot and the thermocouple and blew the dust away from the air mixture hole at the pilot.Worked great!!


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## mmvillar (Dec 4, 2011)

*Problem solved.*

I finally got my problem fixed, although it wasn't the same issue as you.
After a long phone discussion with a tech who really knew his stuff- he told me that while the thermocoupler needs to be continuously heated to keep the valve open, its possible to "overheat" it. That is, the electricity generated by the thermocoupler results from the temperature difference between two halves of the coupler. In other words, the upper part gets heated by the flame and the lower part does not- resulting in the millivoltage. Apparently, my tcoupler was getting too much flame (it was engulfed). I turned down the pilot light and presto, the darned thing started working normally. 
Hopefully someone will read this who can use that knowledge.

thanks for your interest and help.


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## how (Feb 26, 2011)

There is 2 1/2" distance between the hot and cold junction on a thermocouple. Add this to the fact that almost all fireplace pilot assy's are vertically mounted and I'm not sure how you could get the flame of the pilot down to the cold junction.
A small leak from the pilot tube connection to the pilot assy which ignites off the main burner is the most common cause for an overheated cold junction. The second most common cause for cold junction overheating is overgassing or vent restriction which can force the main burner flame down lower than normal.

I'm glad your solution is working even though it puzzles.


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