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  1. #14
    Join Date
    Jan 2011
    Location
    minnesota
    Posts
    22
    I know the gas supply is an issue that has occured prior on other units around this facility, that is still in the process of getting resolved. This unit would not fire at times when I still had 8-9" inlet press. and about 8" between honeywell and maxitrol valve. Is there a setting on downsteam side of the modulating valve (manifold) I should be looking for? Was informed to not even pay attention to this. Was this legitament advice?

  2. #15
    Join Date
    May 2007
    Posts
    730
    I don't pay any attention to manifold pressure if airflow is correct and unit will make rated rise at high fire.

    If the honeywell valve has a fluid power actuator; I have seen a few actuators intermittently run slower than rated when cold and of course if it loses fluid, which could cause a flameout.

    I also wonder what the flame current is pilot only and also main flame high and main flame low. Should be well above minimum when things are right.

    If gas pressure is remotely a problem and hard to catch, I've installed temporary manual reset low gas safety switches to prove or disprove the possibility. Not wired, just connected to inlet gas.

    And then there's the flame sense lead and sensor, if either starts to fail, fine hairline cracking, it can work ok when dry but not when wet. Check the flame sense lead and sensor on high megohms. I use a 60 megohm meter for this, should show infinity if good.

  3. #16
    Join Date
    Jan 2008
    Location
    Jackson, MI
    Posts
    111
    What condition is the ground wire going to the burner. Corrosion will cause sensing problems

  4. #17
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    388
    If this is a direct fired make up air unit the manifold pressure operates in a negative and typically needs much higher inlet pressure to account for required btu output. manifold pressure on these type of burners is super critical. especially on low fire which is what will prove your flame snensor.

    NOTE: On these type of burners you can still have your inlet pressure but not the volume of gas output.

  5. #18
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,288
    Quote Originally Posted by emcontrols View Post
    If this is a direct fired make up air unit the manifold pressure operates in a negative Maybe in low fire some will.....but most end up in positive manifold numbers and typically needs much higher inlet pressure to account for required btu output.What does that means...please elaborate. manifold pressure on these type of burners is super critical.I beg to differ...manifold pressure's are less critical on direct fire units as they are on indirect burners. Not saying ignore them.especially on low fire which is what will prove your flame snensor.That's only true on units with interrupted pilots. Must are intermittent pilots.(which I don't like...but it is what it is.

    NOTE: On these type of burners you can still have your inlet pressure but not the volume of gas output.
    You keep referring to proper inlet pressure but not volume of gas. What do you mean by that?

  6. #19
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,288
    Quote Originally Posted by relay320 View Post
    I know the gas supply is an issue that has occured prior on other units around this facility, that is still in the process of getting resolved. This unit would not fire at times when I still had 8-9" inlet press. and about 8" between honeywell and maxitrol valve. Is there a setting on downsteam side of the modulating valve (manifold) I should be looking for? Was informed to not even pay attention to this. Was this legitament advice?
    I wouldn't worry about it at this point. A couple questions;

    Are you able to see the pilot being lit?
    What is you pilot regulator pressure?
    Is this a interrupted or intermittent pilot?
    Do you know what manufacture of burner is it? I thought those ran Maxon burners.
    If it is a Maxon burner......was the ignitor ever replaced?
    If it was.....make sure the right ignitor is in there. They come in a couple of different lengths, depending on the end plate.

  7. #20
    Join Date
    Aug 2004
    Location
    Des Moines, IA
    Posts
    76
    looking forward to ascj's questions, I had issues with dirty pilot burner at ignition source and igniter points

  8. #21
    Join Date
    Oct 2002
    Location
    Lady Lake, Florida
    Posts
    799
    I'm curious about the fact there is a vfd involved if this is a direct fired make up air unit. I've serviced and started up many Greenheck, Reznor and Cambridge Air units and never had a vfd involved. On my understanding of their desired design and application I would think a vfd would affect the operation. I'm not saying I'm right, just never seen it since burner velocity and exchange of air are critical on those. I would like to hear from others who have.

  9. #22
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,288
    Quote Originally Posted by Trublshter View Post
    I'm curious about the fact there is a vfd involved if this is a direct fired make up air unit. I've serviced and started up many Greenheck, Reznor and Cambridge Air units and never had a vfd involved. On my understanding of their desired design and application I would think a vfd would affect the operation. I'm not saying I'm right, just never seen it since burner velocity and exchange of air are critical on those. I would like to hear from others who have.
    Mostly they are installed, where you have a variable exhaust load in the building. But the OP said it was just used as a soft start, which I have seen also.(But what a waste in money)

  10. #23
    Join Date
    Oct 2002
    Location
    Lady Lake, Florida
    Posts
    799
    Ah Ok . Thanks ascj. for that. Maybe I'll get to see one set up like that since people do see a lot of weird stuff in this trade.

  11. #24
    Join Date
    Jan 2011
    Location
    minnesota
    Posts
    22
    I am able to see the flame fairly good when lit, or burning. Flame looks fine. There is no actual separate pilot for ignition. It lights on low,or min. flame. Once burner lights, and flame is proven amplifire and modulating valve takes over. I did adjust min. fire rate so had suggested reading (1-2 uf) on flame sensor. Do not know if ignitor has been replaced or not, but did clean and set gap to specs. I did try swaping out w/dif ignitor and still had same issue.

  12. #25
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    388
    Quote Originally Posted by ascj View Post
    I wouldn't worry about it at this point. A couple questions;

    Are you able to see the pilot being lit?
    What is you pilot regulator pressure?
    Is this a interrupted or intermittent pilot?
    Do you know what manufacture of burner is it? I thought those ran Maxon burners.
    If it is a Maxon burner......was the ignitor ever replaced?
    If it was.....make sure the right ignitor is in there. They come in a couple of different lengths, depending on the end plate.
    There is no pilot on a direct fired burner. Just the burner unless were not talking about a direct fired burner!!!!!!!!!!!

  13. #26
    Join Date
    Dec 2010
    Location
    Central US
    Posts
    388
    My gut feel is your on the right track with adjusting up low fire gas pressure, it should in turn increase your flame sensor signal strength, but the big question " is it constantly maintaining the proper gas pressure" or sporadically dropping when the building is under a high gas demand condition. I suspect with a known building gas pressure issue that I would strongly urge that be resolved first. ( It is possible that the unit gas pressure regulator may be under sized or sticking. If its outdoors Ive even had them freeze up. All they are is a diaphram with spring) Then see if your still having flame failure problems. I know it sounds strange but trust me on this one.

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