How the fireplace thermopile system is wired 

Thanks for a solid explanation on how these units function. Fought with my fireplace for a while... intermittent flame... pilot light would shut down while in use, etc. I was able to establish that the thermopile and thermocouple were good. Issue was thermopile was not generating enough voltage due to insufficient pilot light. Tried adjust the pilot with no luck. Ended up having to clean out the pilot jet as it became somewhat corroded. ONce that was cleaned it fired right up like it was new.

@grayfurnaceman. This is by far the best video I’ve found on troubleshooting problems with gas fireplaces. The comments and your responses have really helped enlighten me! Thank you sir! Bryan

Thank you so much! we had a repairman come out to look at our Gas Vermont Castings stove and he said the Honeywell Valve needed replaced and they don't make it any more so throw out the stove and get a new one. As that solution wasn't acceptable I came upon this tutorial and we worked on the stove and cleaned it all out and filed the thermopile with an emery board. It works!

Brother. You saved me thousands. Thank you!!!!!

Good video. Thanks for taking the time to train and upload. I replaced a Fireplace gas control on a Hearth and Home unit. The old control had a thermocouple and thermopile. The replacement control, Robertshaw 710 series Millivolt style, did not have a screw in thermopile connection. It had a jumper wire from one of the wire terminals to the place where you normally would screw in the thermopile fitting. I take it, the voltage that operates from the thermocouple is used via this jumper wire to control the magnet on the thermopile side too. ??? I hooked it all up and everything appears to be working perfectly...but that doesn't necessarily make me sleep better.

Your videos are very helpful, thanks very much for your efforts!

Thanks. Really helped me understand what I was looking at. You are very clear and easy to understand.

To anyone this is a thing: only AFTER I installed a million little pieces of rockwool and positioned new logs to make the whole thing look realistic... Did the thermopile decide to start acting up. So an hour later after tearing it all down again I was mystified how the pilot was fully on but didn't light up the rest? Then by chance while in the ON position, a lightly applied pressure to the thermopile to gently push it toward the pilot flame. Money. Seems the connection to the thermopile under it- the screw was loose and held it away from the flame by a 1/16th of an inch...😶 so I tightened by maybe a 1/4 turn. Also, at same time tried rotating the thermopile element so that a different side of it was facing the flame. Anyway maybe TBC maybe but so far so good.

We had a problem where our fireplace would light but not stay lit. We checked the thermopile like you said and saw it was dirty. So we simply took a Scotchbrite pad to clean it and now it works perfectly. If you want to see how we did it, I posted a video on my channel. Hope this helps.

@grayfurnaceman... Hi thank you for your detailed explanation... say if the thermopile is the issue, how do you go on replacing it with a new one... if you have a video explaining that, we would appreciate that... thanks....

This helped us today! Thank you so much for the video!

Gas fireplace that works for 15-60 minutes, then the gas shuts off. Replaced the wall switch, pile, and coupler. Still gas shuts off. Stopped by a local heating business and the owner said that the switch repair is probably the problem. I put a standard 120 wall switch. Told me that the standard wall switch has too much resistance and I need a millivolt wall switch. Went home as instructed and took the two wires and tied together. The fireplace works! Now I have to find a switch.

Thanks for sharing your knowledge! So here's my deal - Mendota DXV-42 gas fireplace, pilot is great (blue, engulfs the thermocouple and thermopile nicely) but burners won't come on. I tested the thermopile output at 289 mV, should be >460 mV per Mendota. I cleaned it pretty good with a scouring pad, but no change. I bought a new OEM assembly which includes the thermopile. It's super tight in there and I might have to destroy the existing thermopile to get it out of the assembly. But replacing the entire assembly involves messing with the gas line, etc (and the screws are almost impossible to get to) and I'd rather avoid that if possible. Also, not only am I having a hard time finding a Mendota approved repairman, I'm concerned that he'll encounter the same issues I'm facing. Before I go any further, is there anything else I should be considering as a root cause?

Thank you so much. This is what I was looking for.

New nova820 valve.. tp to tpth measures 620mv. But pilot solenoid not holding. What to check? I have another connection from pilot unit that threads in and contacts a blue wire... what's that for?

Very helpful. Thanks

Hey Mr.Furnace, The red lead should be th/tp and the white to tp on the valve...If you don't know why....look it up!

Great video!

What is the other red and brown wire attaching on the bottom right side? Where did these wires come from? What do they do?

I liked the clear explanations on this one. My thermopile reads 250 mV when it’s connected to the controller and the pilot is lit. (Not the main burner ) is that too low? I feel it might be going bad because there is a significant delay for the main burner to turn on when the temperature on the thermostat drops (and it clicks on)

Every video I say about Thermo piles, makes it look so easy to replace. On my gas fireplace, it is behind the gas valve, and it’s inaccessible. I’m gonna have to call a gas guy, because it looks you have to dismantle the entire gas valve just replace it

Hi, I have a very similar gas valve. But I can't find the adjustment screw to adjust manifold gas pressure. Is there one? Thanks

First, thank you for all the great info which helped me to diagnose the issue. I have 2 quick questions. My WR brand millivolt gas valve was model was not available. Instead I replaced it with "36C03U-300 400 White Rodgers 36C03U- 333 433 MilliVolt 750 MV Gas Furnace Valve" This new valve has a 3/4 outlet instead of 3/8 for the original and as a result much higher BTU capacity. 1) Is higher BTU capacity an issue ? (previous one was low profile up to 70K BTU and this one is up to 230K) 2) The pilot light is good, but when I turn on the wall switch the pilot light becomes smaller and therefore does not ignite the burners immediately. Is this normal? Thanks

My thermopile is connected to TPTH and TH. Is this incorrect? The wiring to the on/off switch matches on the back

I found problem thanks 👍

Hi! I bought a used cottage franklin propane stove. It fires up and runs fine on low setting. When i try to increase the heat nothing happens...it stays at low heat. I have replaced batteries on remote and receiver. No help! The orifices were changed from gas to propane, so they are new. Any help would be greatly appreciated!

I am looking to convert my gas vent free 10.000 BTU fireplace to thermostat control. My idea is to use a MV Valve from a gas water heater, and thermopile for safety and feedback to control the valve. To keep things simple this would be a STANDING pilot system. This valve would be in series before the supplied fireplace valve. The fireplace valve would be left open. Street value of the manufactured control systems easily approach $700. Any thoughts or suggestion?

Mine is just like this, I set the valve to Pilot but the pilot will not lite at all, No gas is going to it. The gas is on feeding into it. Why do you think no gas is getting to the pilot? Im thinking the valve is bad or the pilot tube/ jet is plugged? thank you

My pilot would not lite, tried cleaning, noticed by trying to lite at the pilot with a lighter that the lighter flame didn't even flicker, so i shut off the main leading into the control box, disconnected the line going into the box, turn the shut off value back on and no gas was coming out, what am i missing here, thank you

Great Video, Thank You, could you tell me what is the Low, High Knob? it lets more air for better combustion?

My 19 year Heat-n-glo has a standing pilot system with a strong pilot light. It started working intermittently. I replaced both thermopile & thermocouple. I turned it on every day for a week & now nothing. Any suggestions?

Hi, my thermopile with wires removed from TH/TP AND TP is 776mv. But the voltage drops to 114mv when i put wires back to TH/TP and TP. This is only with pilot light on hitting thermocouple. I tried jumpering th/tp and th but burner not on. I tapped valve lightly and burner came on. Is it a bad gas valve? Thank you.

My thermopile voltage is .390 mV with the pilot on. When I turn the burner on it dropped to .180 mV. My question is it normal for it to continue to drop while the burner is on. In 17 minutes it dropped to 157 mV. My main issue is that it intermittely has shut the burner and pilot Off. Restarting the pilot always seems to work, but not the burner. One of the times when I turned the switch on, the pilot shut Off. I then cleaned the thermopile with emery cloth and everything seemed like it was working great again until the third time I tried it and the burner wouldn't light again.

Need Help: I have Intermittent Heatilator Gas Fire log Model# ND42361. I have two wall switches. When I turn the 1st wall switch (power) nothing happens but after turning the 2nd wall switch the pilot comes on and stays on but the burner does not. I have: Replaced the IPI electronic ignition control module & A/C Wall Adaptor. Cleaned burner holes and heat sensor (flame is close to heat sensor - heat sensor turns red) . I will truly appreiciate if anyone can let me know what other troubleshooting I can do to get the burner working ? Blessings

Why does my natural gas fireplace vent free insert thermostat work backwards

Do all thermopile systems contain electromechanical safety controls to shut off the gas if the pilot light isn't lit?

i have a majestic dvt39 propane fireplace. I have low flame. Service guy told me the millivolt gas valve was bad, so I purchased a new gas valve, same part #, brand etc (SIT 820 NOVA 0820651 for propane). I'm going to replace it and was just wondering if there is anything I should be aware of before I do this? It looks pretty straight forward and I've read what I can find and watched several videos etc. . But just wanted to cover all my bases before I start. From looking at it the biggest issue is going to be getting the old one disconnected. it's black iron (6in nipple) from the shutoff valve, into the valve. There is a coupling, but not sure I"ll be able to get wrenches on it to loosen it as it's right under the fireplace and it's tight in there... but anyway.... just wondering if there are any 'gotchas' to watch out for. thx in advance

Hi maybe you can help me the main propane supply line for a hot water tank burner assembly What should be in the tube

Where are you located I would like to learn from you. I would like to be able to fix fireplaces.

GFM. I'm having a weak pilot light problem on a Majestic 36BDVRRN natural gas fireplace with a Sit 820 gas valve and an FP 9903 top mount pilot. It is burning blue,but is not strong enough to be projecting out far enough to impinge on both the thermocouple and the thermo-pile. I proved everything else was working using a propane torch to substitute for the standing pilot. I've tried adjusting the flame using the adjusting screw on the gas valve, but there was no change. I use compressed air to blow out around the head of the pilot tube as much as I could, but that did not seem to improve anything. There did not seem to be any easy way to disassemble that unit to try to get to the orifice to check for plugging, assuming there's one in there. What would be the procedure to do that? I also tried removing the pilot gas tube from the main gas valve and was going to blow compressed air through that to see if I could remove any obstruction. I was able to get the ferrule not completely loose in the, but the small diameter aluminum tube did not seem to want to pull out of the gas valve even with pretty firm tugging on it. I did not want to damage it so I did not mess with it anymore and just retighten the ferrule nut. Is there some special trick to remove that pilot gas tube? Looking at the photos online of the replacement pilot head assemblies it appears to be just a simple tapered end on the tube that would match up with a seat in the gas valve.

Spent a lot of time on your video. I have my multimeter dial turned to 2 mila-vaults setting the readings I am getting is -.523 with thermostat off and -.075 thermostat on. Is this a good reading?

My main burner does not turn on. I have 478 mV with pilot light ON. When I engage the wall switch-thermostat I read 33 mV. Way below the minimum requirement. Would this prevent the main burner from turning on? Does this indicate a bad thermopile needing replacement, or do I need to do more testing? Thank you

The hi/lo control valve on a Robert Shaw is stuck on LO! How does one fix that issue?

So about the "limit switch" shown @ 3:25. My stove shuts down after ~10+ minutes. Cools down and relights. So seems like limit switch intervention. How do I know if it's defective or if there is an actual problem? (Hearthstone Tucson 8700)

my 95 year old grandmother was given an older U28 Regency fireplace. She wants it working so she doesn't have to have wood brought in for her wood stove. I don't know if it's hooked up right or if it works correctly. I don't know anything about gas stoves. Can I inspect it to make sure it works correctly without having the gas company turning on her gas? she doesn't want a gas bill if this fireplace doesn't work. I don't know what to check for.

Hi, Why do some have a Thermo couple & a thermopile?

Is there a way to wire in a thermostat on my gas fireplace mine has a gas control valve with pilot, on ,and off and another knob that controls the flame height it also has a box with a switch that says on off and auto I realized to Day there is a light switch on my wall that I can turn the burner on with when the box on the heater is in the off or the auto position or I can turn it on by switching the box to on ..... any help would be appreciated thanks

Anyone can explain to me why some pilot assemblies have thermocouple only, some have thermopile only and some have both of them???? Thanks

Hi Gray in my job the have a Vulcan gas grill 4 burdn, 2 thermopile do not stay on the 3rd thermopile is on but do not fire the register,the 4th O.K please help me thanks

Hello, I have a thermopile issue I tested with a Multimeter and open flame and as soonest I hit 400mv meter goes OF.L (Offlimit)..as I let it cool then It starts working again. Does that indicate a faulty Thermopile? My fireplace pilot would not stay lit. Thank You

I have an issue where the flame above melted the igniter ... any thoughts why that would get so hot in that area?? Air flow issue? I think it’s tripping the high temp limit switch (spillage )

question: I light my pilot after cleaning my thermopile it has improved blowing blue/strong but won't light the rest of the fireplace. It's at 663mV . The sensor lights and becomes bright red...after several minutes the sensor suddenly cools off and the pilot loses it's zing, but still burns well. Any ideas?

exc. demonstration

What if the voltage is 550 mvolts with switch off and only 10 millivolts with switch on. Does that mean my thermopile is bad?

very confusing, to me, markings on gas valve terminals. Not your doing. Also see 4:03, I don't see a mark for the gas valve connection. Otherwise thanks for all information.

my 4 year old Regency u-39 propane stove will at times stay on heating the house beyond the set temperature, as high as 90 when set at 70, this happens occasionally , I replaced the batteries in the wireless remote and receiver box, but with no luck....any ideas? thanks

How do I supply power to my heat and glo natrual gas fireplace? It won't run unless it has battery's in

My bradford white water heater is giving me a code led probe,will that be the thermopile?

I turned on and it stayed the same. Does that mean it’s broken?

my furnace start only when the thermostat is all the way up, and then it sounds like it lit up then immediately it goes out. then the gas smell. what is wrong with it ???

how can I TAKE OFF THE NUT TO GET IN SIDE VULAN GAS 4 BURNERS

I enjoy your videos man. You've got some great knowledge on your channel. See if you can help me, please. I just bought a house with a propane fireplace. It's run off of propane, with a Sit millivolt valve. The pilot light looks great, all blue flame. I can not get the burner to come on. The fireplace has never been used, house was built in 2014. Should there be electric an electric switch to give it power? I've replaced the thermopile, only to get the same response- No burner flame. ____HELP!

Gas fireplace;......my pilot stays lit but when I light my burner it only stays lit for about a minute or less and then you hear a "click" and the burner and pilot go out. Do you think this is a limit switch issue or?................could you share your thoughts

Gray is the safety always wired in line with the thermostat? To me I would think so. If not could you explain the reason it would not be please.

Hi. If the thermocouple or Thermopile is not generating enough millivolts. Do you need to replace the whole pilot light assembly or can one just replace the thermo couple and pile?

does the polarity of the thermopile matters?

I have a problem with my Napoleon HD40. The pilot lights perfectly every time but the main burner doesn't light. I'm not sure if the problem is with the Dexen IPI 3v electronics not sending the correct voltage to the valve, or if the Dexen valve isn't opening when told to do so. The thermopyle is sending about 480mv to TP-TH/TP. It reads about 340mv between TP and TH. With no wires connected the resistance between TH and TP is essentially infinite (open). Does this sound like a electronics problem or a valve problem? I've been trying to fix this for months . . . and it's about to get cold up here in Canada! Any advise would be appreciated.

How do you know you have a open circuit when your in mV, wouldn't your meter have to be set to ohms to perform a proper resistance check?

Gray Furnaceman I always have to manually turn on my fireplace it has the thermopile system I use the igniter to turn on the pilot then I wait for the fireplace to light up sometimes it takes days and then it just keeps burning until I close the gas valve any thoughts of what I can do to correct this problem before calling in a repairman

Hi Gary, nice video. I have a gas fireplace that is currently hooked up to a light switch. So "on" the fire will light... "off" and the fire goes out. The problem is I am scared we will forget to leave it on accidentally while out of town. I am attempting to replace the light switch with an analog low voltage thermostat so the fireplace will turn off at a max of 80 degrees. I hooked up the red and white wires from the switch to the thermostat from honeywell and nothing happened. Any guess as to why? Is the voltage not quite right for the model thermostat (CT87K)? or is the wiring at the control valve not set up for thermostat control? Seems like mine is wired just slightly different. Thanks for any help!!

What's a thermopile?

Completely useless video, doesn't explain anything. He mentions a bunch of facts but doesn't explain any of them. And why is there a plastic bag stuffed in the bottom of the fireplace?? You won't learn anything from this video except that there's something called a doohickey.

That was a very poor explanation, really why take the time