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  1. #1
    Join Date
    Oct 2002
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    Lexington, NC
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    Buck Gas Logs-Intermitent problem

    Worked on a set of gas logs yesterday for a gentleman. Don't know a whole lot, though I have worked on logs from time to time, but usually it is the thermocouple needing attention or a problem with the thermopile or too much resistance in the control wiring, etc.

    Initial problem according to the customer is that the logs would cut off after about 15 minutes of run time. When they turn off, it cuts the pilot and main off. I found the thermocouple to be very dirty, so i cleaned it with sandpaper and cleaned the thermopile off as well. So I was thinking that if the this is like regular gas valves, the thermocouple for the pilot is not producing and is droping out the valve, which will cut off the gas to the pilot and main burner.
    So here is the tricky part. The fireplace door is always open. After I finished yesterday, the unit ran for 1.5 hours, and then turned off. Well the initial complaint was that if they take the front logs off, it works fine and doesn't cut off. So the guy takes the logs off yesterday evening, and the unit has worked ever since. The unit is 10 years old, and I don't know if they had the oxygen depletion set ups back then or not. I did not get the model number of the stove, and none of them on the buck sit looks the same on the log setup. The logs don't seem to be changing the shape as the flame, or at least the flame isn't impenging anything other than the top part of the thermocouple. The unit is setup with a remote control. That is all I can think of that may fill in a couple of questions.
    I guess what I am down to is perhaps there is an oxygen sensor on this and it is cutting off the unit. I am not sure if those turn off pilot and all or not. Otherwise, it appears to me to be a weak thermocouple.
    I guess my questions are -Did they do the oxygen sensors 10 years ago, is the pilot flame adjustable on these small valves, and what would make the unit work without the logs and turn off intermitently with the logs in place?
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  2. #2
    Join Date
    Aug 2004
    Location
    S.E. Pa
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    Cool

    No offense but if you aren't familiar with these systems then you really should not be working on them. Take an NFI Gas course when you can to familiarize you better with the hearth gas products.

    Everything starts with identifying the unit. Until then, you are spitting at the wind............or playing with fire,explosion and CO more appropriately. You must locate the rating plate, which will identify the mfr. model, serial #, which fuel it is set up for, orifice size, BTU input rating, safety listing standard and the listing agency along with basic operating directions.


    A pilot dropping out could be from a lot of things not limited to but including: low inlet pressure, gas piping too small, dirty pilot orifice and burner, vent obstruction, problem with combustion air, secondary air pattern problem, etc.

    Prudence is the better part of valor. Refer them to a qualified tech.

    ODS pilots have been around since 1980. If this is a ventfree appliance then is it a Vf logset? If so, you should not have glass doors in front of it in the first place.

    If you cannot locate a rating plate, you should treat them as unlisted logs, shut them off and remove them.

  3. #3
    Join Date
    Oct 2002
    Location
    Lexington, NC
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    5,157
    I have done well learning on HVAC talk for the last 10 years, and have worked on boilers with burner cones larger than these logs, so I think I can catch on with an understanding of these valves and just what can and can't be adjusted.
    I called Buck Co. today with the model number and the tech there told me that they had some get out of the factory years ago that the thermocouple and thermopile weren't contacting the flame good enough. He told me how to adjust it to. Otherwise he said that he thought it to be a thermocouple problem, as I have a good pilot flame. He gave no relevance at all to the log placement causing the intermittent problem.
    Now, what I noticed after making these adjustments was that when the unit lit the main burner, the flame on the pilot droped down a little, making it's contact with the thermocouple less surface area wise. I was hoping to have the flame contact the thermocouple more during main burner operation. And this being the case, with the convection effect of air movement into and around the flame with the heat currents, the pilot light seemed to move around a little.
    Now I do have a pilot adjustment screw, but turning it did not seem to help the flame. I did blow out the pilot tube, and I did not find any materials inside of it. As I said, the flame is good.
    What I have not found on any of the valves of this style is the main burner screw adjustment. I did locate the test ports, and no, I did not check them today, but the unit is Natural gas, and I think the plate said 4.5" w.c. for the minimum pressure. I will check it, but as good of pressure as I got off of the pilot outet without the tube on it, I feel confident I have enough pressure into the valve.
    Once again I appreciate help, as to where to learn more about these valves, etc. I have a lot of experience on gas furnaces, etc., and I find it hard to believe that there is anything magical about working on these logs, especially being that I seem to know more about the effects of high resistance on the millivolts DC voltage circuit than some of the posts I am reading here. These logs have worked for 10 years, so I feel confident my HVAC talker friends can assist me in figuring out how to get them working again.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  4. #4
    Join Date
    Aug 2004
    Location
    S.E. Pa
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    Question

    I thought you said you failed to obtain the model number now you claim you gave it to the mfr. So what is the model number? What make valve does your unit have?

    You cannot tell inlet gas pressure by looking at a pilot flame. You need to connect a properly calibrated manometer and test it static, burning then with the house under full load to see if you still have your minimum inlet pressure. The main burner adjustment is controlled by the manifold pressure regulator. You sure you should be working on this appliance? one of the magical things about these appliances over your typical boiler or furnace is secondary air and logs. As you noted, the 'convective' air currents do affect the pilot flame and thus TC output. This is secondary air btw. Secondary air can be affected by the venting, logs, inlet air temp, and other things.

    I went on the Buck website and most of their logs are VF. If this is VF, you can NOT adjust the pilot flame. These units are rigidly engineered and non field adjustable. BTW, if you try to ream out an ODS pilot, you can ruin it.
    Last edited by hearthman; 01-24-2012 at 08:38 PM.

  5. #5
    Join Date
    Oct 2002
    Location
    Lexington, NC
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    Can't learn if I don't get dirty.
    I went out to the property after I posted. As you say, it is useless to try to go any further with it. The unit was old enough that the tech didn't seem familiar with the name of the log, which in this case was the model number. The logs are by Buck.
    Model Timber Glow and the Serial is 00470.

    I know I should have checked the pressure with my Testo, but I wasn't really thinking along those lines of problem areas. The only problem that I have noticed with the burner is when it lites the bottom second, which lights last, it lights really hard, almost blowing itself out on the lower burner only, and then lits and burns fine. Now I had mentioned doors, and I don't know if it has glass doors as up till now I have not been tuned in to look for that, but I do know it has the flexable mesh screens because they kept getting in my way.

    So I am reading up on these valves in general, and would appreciate the makers name so that I can do some real research on them, but I am learning that the valve adjustment is done at the factory internally speaking, and as you say the rest is with the regulator, so that is good info. I have taken gas pressures off of this type of valve on a stand alone unit, and really didn't learn much on that one because I saw a pressure problem, went to the LP tank and found it only one quarter turn open. But yes, I am set up to take that pressure when I return.
    The customer has told me that he wants me to go ahead and get a new pilot assembly being there is some concern at the factory about that ones positioning, and if nothing else it has now been tampered with, even if under their instruction.

    So doing a little digging, and have found this comment in an article on thermocouples, which I find interesting. "4. Overheating: If the unit works for a few hours and then shuts down, it’s possible the thermocouple has become overheated. Repositioning of the gas valve and/or pilot may be needed to avoid this problem.". I have never heard of a thermocouple overheating, though I do see them from time to time melted looking on the tops.
    One thing I find of interest and think will be key with this unit is the question of how much of the small thermocouple should be in the flame. I told the rep that just the top of the thermocouple was in the flame, and he said that is right, but when I said that, I meant that JUST the top of the thermocouple was in the flame. I really think the flame is being pulled off of the thermocouple during main valve operation, but at the same time I have noted that there is a pretty lengthy delay in the time that the pilot valve closes and the time that the flame is turned off with the pilot control, so it would seem that even a dancing flame would tend to keep the logs lit.

    Anyway Hearthman, I appreciate any help, and if you want to PM me the info to keep it off of thread will be ok.

    And one other thing to note is that the owners leave the control setting to the lowest position on the main valve, and the pilot is turned all the way in. That is the way I found it. I wasn't sure exactly how the pilot adjustment worked. It seemed to be the screw was the adjustment, whereas on a furnace valve there is a screw under a cover screw. I let it be when I didn't really see a difference with adjustment.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  6. #6
    Join Date
    Dec 2011
    Location
    PA
    Posts
    201
    What does the pilot flame look like while unit is burning? does it remain smooth or does it look like the pilot starts to get rough and gurgle? if the latter you could be experience below min gas pressure and/or, dirty/dusty ODS pilot. when you put the front log in, you change the secondary air pattern in and around the pilot, which could be cause the ODS to trip, if this is the case make sure the log is position properly and that the ODS pilot is cleaned.

    Oh forgot to mention the flame contacts the very tip of the TC on most ODS pilots and in a lot of case even lifts up just a bit to where it's not touching the TC this is OK and normal.

  7. #7
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    Aug 2004
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    Cool

    Ok, we're getting somewhere. This is a ventfree so it has an ODS pilot. Yes, it has a small fixed pressure regulator for the pilot and another for the burner manifold pressure. The pilot is non-adjustable. You're not even supposed to bend the TC tip into the flame. That's part of that heavy pilot bracket maintaining the alignment btw pilot burner and TC.

    You can make sure the pilot is clean: blow it out with canned 'air'. Also, about 3-4" behind the tip of the pilot burner is a primary air hole cross-drilled through the pilot burner. It is usually 1/8". You can blow it out or use a pipe cleaner. Just do NOT poke down inside the pilot orifice or you'll ruin it.

    If the entire pilot gets too hot, the TC can drop out. Remember, you need a 400F differential btw hot and cold junctions for a TC to work. Otherwise, you may have the pilot dropping out due to oxygen depletion. You can prove this using a combustion analyzer. If you can watch the pilot flame on dropout, it gives a lot of info. If the flame curls yellow and short, it is dirty or low inlet pressure. If it advances past the TC it is oxygen depletion.

    HTH,

  8. #8
    Join Date
    Oct 2002
    Location
    Lexington, NC
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    It is speratic turning off, as it has not turned off with me there, so the info at turn off won't be easily had.
    When the main flame isn't burning, the pilot flame is on the large side, and actually touches a piece of factory bent sheet metal right over the assembly. Now when the main burner comes on, the pilot flame drops off a little. I don't know that I would call it rough, and it doesn't do the thing where it blows past the thermocouple. It actually pulls away a little from the thermocouple going back toward the pilot orifice. The flame seems to kind of dance back and forth from time to time, which is what makes me think about air currents. It doesn't move way off of the thermocouple, but if it touches when it drops off, it isn't touching much.
    The part that the tech support told me to move was actually the thermopile, and I am not going to argue with the tech support, but I don't see what that has to do with the pilot other than one point he made, which I will write in later in this post. But I asked him if the thermopile not producing enough voltage and droping out the valve could take out the pilot and he said yes. I don't understand that. I understand the thermocouple shuting off both the main and pilot, but the thermopile should only turn off the main valve to my understanding.
    Anyway, he told me to take a screwdriver and pry up on the rear of the thermocouple to push it down into the flame more for more flame contact. When I questioned what this had to do with the pilot, he said that it may help to push the flame down on the thermocouple a little more.
    What this actually did was to give the ignitor spark a path to the thermopile instead of the thermocouple, which made it harder to light because the spark wasn't in the path of the pilot gas stream. At least that is what it seemed like to me. But I am learning this equipment, so I may be off on some things.
    So why do they have a pilot screw if it is preset? Is there a set screw under neath that brass screw?
    So lets go this route. I am going to purchase a new pilot assembly from Buck for about $40, as I am not sure if they sell these generic to fit their units. So I put this new pilot assembly on, I confirm the proper minimum gas pressure at full flame, I have the same log setup as the unit was sold with, and if it has doors they are open. Shouldn't the logs work being they are back to original condition?
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  9. #9
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,157
    Talked with Buck tech this morning to order the pilot assembly. Asked if they had any info on working on their gas logs, and he said it is just in general info like all the other logs. Are there any books on these things?
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  10. #10
    Join Date
    Dec 2011
    Location
    PA
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    not really. new pilot is a good route though, the ODS pilots are very sensitive to dust, dirt, buildup of random crap and just wigging out.

  11. #11
    Join Date
    Oct 2002
    Location
    Lexington, NC
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    Changed the pilot assembly today. Checked the gas pressure at Inlet 8" w.c. and 3.75" w.c output. Adjusted it down on till the output was 3.5" per specs, but that took the input down below the 4.5 minimum available, so I bumped the inlet up to 6" and let it ride at 3.60" high setting. They run it on low, and that was down to around 2" w.c.. Since adjusting the pressure, it does not start hard on the front burner, which was basically lighting, blowing itself out and relighting, making a bit of a poping noise.

    If they had an adjustment screw on these valves would have been helpful.

    So the biggest difference I saw with this pilot was the flame was stiffer and went straight out. But doing this, it did not touch the thermopile. I checked the DC out put on the thermopile and the thermopile had to get up to 350 millivolts before it would open the main valve. Working DC voltage was 160 millivolts operating. I don't think this is going to be a problem, since they leave the pilot on all the time, but if starting cold it takes about 1.5 to 2 minutes to heat up the thermopile enough to open the main valve. Usually I have been seeing something like around a 15 to 30 second delay at most. Wasn't really sure if this was good or not, and being that the factory tech the other day told me to push the thermocouple down into the flame on the old pilot assembly, I was a little baffled that the thermocouple wasn't in contact with the flame. I left it alone because it is how it came to me, and the pilot isn't adjustable, so it is what it is. I am hoping to get some input on this point from you guys. As long as it keeps the valve open, I like it better operating outside of the flame.
    Good news is that I haven't heard anything from them, and it has been about 8 hours, so I think that got it.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  12. #12
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    PA
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    Yeah it sounds like you got it. I'm not sure about the flame not hitting the TC Usually most just skim the very top of the TC. But if it works, it works!

  13. #13
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    Quote Originally Posted by darthvader View Post
    Yeah it sounds like you got it. I'm not sure about the flame not hitting the TC Usually most just skim the very top of the TC. But if it works, it works!
    It does touch the thermcouple, but does not touch the thermopile (generator). Before it was barely grazing the thermocouple, and touching the thermopile on the last 3/8 of an inch of the cylinder.

    It seems that there isn't as much help on this part of the forum. Is there a reason for that? Usually hvac talkers are back and forth with information and trying to better each other. On this part of the forum it is like pulling teeth to get info.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

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