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Tom, HVAC Technician
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Experience:  16+yrs HVAC/R service. Residential Commerical Industrial
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I have a monessen ventless gas fire insert (DLX 28). Pilot

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I have a monessen ventless gas fire insert (DLX 28). Pilot light doesn't like to stay lit. Most likely the thermocouple?

Hi, Tom here.


Does you DLX 28 have a thermostat or is it manual control?


Let me know,


Customer: replied 6 years ago.
Manual Control (ie, on/off). I can control the size of flame, but that's it. The pilot light lights up fine, but won't stay lit--most of the time. It's lit right now, but will probably go out in the next few hours. I thought it might be a thermocouple. I see no other loose connections. Thoughts?

The thermocouple you have is what is called a pilot generator. It produces the voltage to operate your gas valve. It has to be producing 600 -700 millivolts d.c. for it to operate. Since this is way less than 1 volt, it needs to be in good tune to work.

See full size image It will look similar to this.


The first thing you need to do is look at the pilot flame itself.

It needs to envelope the entire end of the pilot generator.

Look for a good crisp blue flame. If you have a lazy yellow flame that curves upward and doesn't envelope the end of the generator, it will not heat it sufficiently to produce enough voltage to hold in the pilot valve.


If that is the case, a good cleaning of the pilot burner is in order. Use a small stiff brush, some folks have used a pipe cleaner and some compressed air to clean any dirt, soot , debris away from the pilot orifices.


This should take care of it. If not, you may have a faulty pilot generator. I would test the output of the current pilot generator before replacing it. It would require a decent digital volt meter capable of reading dc millivolts. If you are not able to test it, replacing it would be the next step. A faulty gas valve would be the last option, but fairly rare compared to the pilot issues discussed above. A fireplace shop or maybe even a decent hardware store should carry a new pilot generator.


Check the easy stuff first. Let me know if you have further questions. Thank you!



Customer: replied 6 years ago.
Thanks. Awesome stuff. I will pay, but have a few follow on items.

It's not the flame. Flame is perfect.

I put a multi-meter to the thermocouple and watch the voltage increase as the thermocouple heats up and decrease as I cut off the gas and the thermocouple cools off. I notice that as the millivolts pass through ~40 the pilot light will stay lit. My problem is that it takes least a lot longer than last season...minutes vice seconds.

Do you think this is the thermocouple going bad? Like I said, the flame is excellent.




To make sure we are on the same page,,,thermocouple produces about 30 millivolts, a pilot generator abou 6 - 700. Does your thermcouple have leads or does it screw into the gas valve body?



Customer: replied 6 years ago.
It has leads (???) that go to the gas body. I think we are speaking the same language. I guess it is a pilot generator...although the book talks about a thermocouple on the ODS body??? Anyway, it's working right now. Any other thoughts?

Yes, we are almost on the same page. A pilot generator will have 2 wires to connect to your gas valve. The thermocouple is a somewhat stiff copper tube with a nut on the end that simply screws into the gas valve.


It is possible that the pilot generator is getting weak. They do that. I always check 'open voltage' which means I disconnect it from the valve altogether. Put my volt meter on the 2 wires and then light the pilot. You'll have to hold the knob down and watch the voltage. It takes about 3 hands and a little luck. Or a couple of jumper wires.


Anyway, when up to full temp, the generator should be making 600 -700 millivolts with 'open voltage' not hooked up to the valve. Anything less than that is going to cause you trouble and should be replaced.


Thanks for the good questions. I hope you get it going.



Tom and other HVAC Specialists are ready to help you
Customer: replied 6 years ago.
Ok. I did what you said, and it sounds weak. Seems like a self-help replacement will be pretty easy. Any tips?

I appreciate the help.


No, not much. Pilot generators are all about the same. Take your old one along, just to make sure it is about the same size.


I think you can reply to these posts for about 30 days, so feel free to reply if you have further questions.


Thank you for the accept, I will leave positive feedback.


Tom :V)

Customer: replied 6 years ago.
Just to make got your money, right? Website is slightly confusing.

Yes I did and thanks for the bonus!


I understand about the site. The first time I used it to get advice on my Chevy van I was totally confused. Second time, much better. Just have to figure out the quirks I guess. That is why I'm pretty upfront about not paying until you get an answer that is helpful.


Thank you again. Tom

Customer: replied 6 years ago.
Thx, Tom. Have a great day and Happy New Year!

You're welcome, same to you and yours.



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