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  1. #1
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    Oct 2015
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    York GY9S100C20DH11K – runs for a minute and then drops flame.

    I’m having a tough time with this split system. This is actually a residential York gas furnace is installed in the ceiling in an office building. Access is very tough. It’s in a drop ceiling and they put a 4’ light right in front of the unit.

    This is a 90% gas furnace with a hot surface igniter. Single stage gas valve. The unit is mounted horizontally above the drop ceiling. There is no gas valve at the machine so I’ll have deal with that as well.

    Like the title says, the symptoms are … the unit fires and burns ok for like 30 seconds to a minute. Then I hear a relay click on the controller and the flame goes out and the unit almost immediately turns on the hot surface igniter and re-lights. This repeats and eventually the unit locks out – code 8 as I recall – ignition lockout.

    Here is what I know.

    1) The pressure switches are ok. There are actually two pressure switches and I waited for the inducer to start and jumped them out – same problem.

    2) I don’t see any real effect on the flame as the indoor blower starts up – but it’s tough to see the burners. I don't have any real reason to suspect the heat exchanger at this point.

    3) The flame sense current – per the test terminals on the controller – is steady for a while and then it bounces all over the place – drops to zero periodically. OK - looks like the unit is having trouble sensing flame.

    4) I replaced the controller and flame rod – same problem.

    5) Inlet gas pressure is 7.1 and outlet gas pressure is 3.6. Seems to be steady.

    6) I can see someone has already remove the flex gas line and replaced it with a larger diameter length of Wardflex. Looks like someone else was trying to deal with this issue. Seems like gas pressure is fine.

    7) It’s difficult to observe the burner while the unit runs due to the location of the air handler. I can now see the unit is actually dropping flame for a fraction of a second on the lower burner only.

    8) The unit has 4 burners. The bottom burner (closest to the gas valve) is the one with the flame sensor. By the way, there is no provision to move the flame sensor to another burner. I took a video and I can see the bottom burner momentarily losing flame. It’s very tough to see but the video seems to pick it up pretty well. It’s very fast – just a fraction of a second. So the bottom burner periodically does not have a steady flame and it appears to be enough of a disruption so that the flame sensor/controller sees this and turns off the gas.

    So given all this I am assuming that the gas tube or orifice might be clogged. I tried to inspect this without completely removing the gas valve and burner assembly and the burners seem pretty clean. I’ll have to turn the gas off to the building and install a gas shutoff at the machine before I can actually remove the whole burner assembly and gas tube and then I can really see that lower orifice. Someone mentioned that this could also be a symptom of a heat exchanger problem. Anyone see anything like this? If you have a guess, let me know.

    I’ll be going back with a more senior tech. I have no idea how we are going to get the access we need to work on this unit.

  2. #2
    Join Date
    Mar 2013
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    Billington Heights, NY
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    could be an exchanger problem but that would be effectively bypassed when the pressure switches are. get your manometer on the valve/manifold. a drop in gas pressure could do that. debris in the orifices could. you really need to pull out everything and visually inspect and clean it.

  3. #3
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    Dec 2000
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    Victorville Ca
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    After doing everything you did I would think it could be starving for air. If sealed i would try and open it up and see if you lose flame, I have had problems with 90' if not mounted near level . Factory told me once on a upflow that I should be off bibble with the furnace tilting just a tad forward. Water in the tubing and backing up a little

  4. #4
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    Oct 2015
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    New Jersey
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    Thread Starter
    Quote Originally Posted by Roncool View Post
    After doing everything you did I would think it could be starving for air. If sealed i would try and open it up and see if you lose flame, I have had problems with 90' if not mounted near level . Factory told me once on a upflow that I should be off bibble with the furnace tilting just a tad forward. Water in the tubing and backing up a little
    I forgot to mention. The air box is open. Prior techs already removed the intake pipe so the unit was already pulling air from the space. I took the burner box cover off - same problem. It's still open but it should be getting enough air. Ultimately I would like to re-attach the air intake pipe but I'll leave it open for now.

  5. #5
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    Oct 2015
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    New Jersey
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    Thread Starter
    Quote Originally Posted by HVAC_Marc View Post
    could be an exchanger problem but that would be effectively bypassed when the pressure switches are. get your manometer on the valve/manifold. a drop in gas pressure could do that. debris in the orifices could. you really need to pull out everything and visually inspect and clean it.
    The pressure switches do not seem to detect any problems. I had my manometer on the gas inlet and outlet and the pressures look good. I have no idea whether my manometer would really see a momentary disruption in gas pressure but I'm not seeing that on my Fieldpiece SDMN6 - gas pressure looks solid. Like you said, I think the next step is to get that burner assembly and manifold apart and clean it all up - we'll see when they send me back. Gotta install a gas shut off first.

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  7. #6
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    Oct 2015
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    Thread Starter
    Quote Originally Posted by HVAC_Marc View Post
    could be an exchanger problem but that would be effectively bypassed when the pressure switches are. get your manometer on the valve/manifold. a drop in gas pressure could do that. debris in the orifices could. you really need to pull out everything and visually inspect and clean it.
    OK, I went back today with a senior tech. This would have been tough for one guy to diagnose on his own. Fired up the unit and it stayed lit for a few minutes. So now we had try to initiate the failure. Right away he suspected gas pressure. Hooked up a manometer and the pressure was fine. I went around the building and started firing up the other furnaces one by one. As the other furnaces fired he did eventually see the unit drop flame and re-light. He was also able to see a large drop in gas pressure on the manometer.

    His conclusion – the unit is ok, it’s the gas regulator – so the customer will have the gas company come out and change the regulator.

    So we will see if this fixes the problem. I will be able to go back and fire this unit up and then fire the other units and see how it does.

    I have no problem with this diagnosis but if it is indeed the regulator the symptoms and perhaps even the regulator performance changed from day to day – based on temperature it appears. The problem was first reported on a really cold day - the unit did not stay lit very long at all. When I worked on the unit earlier in the week it was warmer. It was running for a while and then dropping but I never touched the other thermostats. I'm not sure if the other units were running. Today it was warm - the other thermostats were satisfied so the other units were off. So this was not so cut and dry. But at least we have a valid basis to have the regulator changed. Perhaps this will fix it – or maybe there are some other issues, maybe the gas piping is not sized properly. We’ll cross that bridge when we come to it.

  8. #7
    Join Date
    Nov 2006
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    Southeastern Pa
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    Okay, let's step back for a moment.

    If you have one regulator...the gas Co regulator...for the entire building, it means the entire building is running low pressure gas service.

    SO...if you have piping that is too small, you cannot move enough gas to run all of the units, and that is why the unit is seeing a drop in pressure when the others fire.

    This is a MUCH bigger problem than an adjustment.


    I have a customer that had six new RTU's installed last April. It was a new store, and we had not yet been assigned as a service contractor.

    The installing contractor ran 1" piping all around the roof and down to the meter. Luckily, he installed a regulator at every unit. The gas had not been turned on, and so they called the Gas Co and had them come out and restore gas service.

    Turns out the gas service was only about 5"wc. Not enough to get gas to six units through 1" piping. There were two choices: upgrade the meter rack to 2 psi, or upgrade the piping to 3". Kind of a no brainer, yes?

    About three weeks ago, the client finally got the gas Co out to change the rack pressure to 2 psi, and that solved the issue.

    In your case, they "could" have their gas pressure changed, IF the main is not a low pressure main. Then, you guys can install regulators at every unit. That would solve your issue.

    BUT, be warned...if they plan to do this, you MUST install the regulators BEFORE the gas pressure is raised. Otherwise, you kill all of the gas valves.

    It is very difficult to coordinate a visit with a gas utility, and just turning off hand valves at units is not a solution, because someone else can turn them back on.


    Adjusting the gas Co regulator will probably not help.
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  9. #8
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    Nov 2011
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    gas companies won't admit it, but they change service pressures with usage. really, they have to....in the summer, there's WAY less consumption....winter rolls around and there's a HUGE demand on the system. Personally, I don't think those changes are automated. I think local and regional service guys have to make them. If they haven't cranked up the system to match demand you could have an entire area with lower than normal pressure.

    I had that happen in an entire subdivision. it was right around the seasonal cold shift. I couldn't get more than 9" out of the gas meter. They called the gas company, he checked the meter, said it was fine and left. Magically, a few hours later, 14". Customer could run all their gas appliances at the same time again.

    I'm skeptical that system pressure is your problem.....especially if that is the only unit experiencing problems.

  10. #9
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    Nov 2006
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    No his problem is not system pressure. He has a piping problem for a low pressure system, which can be fixed if the gas utility can convert his meter to 2 psi.

    If there are two meters on the rack, and one is for a different customer, he is stuck. They won't change pressure where a second customer is involved.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  11. #10
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    Depends on how current the problem is. Did this just start on a older existing system or has it been a problem from day one.

  12. #11
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    Oct 2015
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    Thread Starter
    Thanks for the great info. We will see how this plays out. This strikes me as a problem that is not new. I’m not sure whether these systems ever ran right.

    Luckily, this is a small stand-alone building. We have a single meter with a single regulator feeding this place. The meter is new but the regulator looks like its original to the building so it’s old. Four residential gas furnaces in the ceilings … three 100,000 btu and one 60,000 btu. There is at least one hot water heater too. So we are probably right around 400K BTU for the gas appliances in the building.

    The senior tech and I discussed the fact that the gas piping may not be adequate. It’s all hidden in the walls. This building has no basement. If the regulator does not address the problem, we will have to look at the gas line in more detail. We just might have to increase the gas pressure and put a regulator at each unit as suggested above. The regulator is getting changed first, then we see if the systems does any better.

  13. #12
    Join Date
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    We don't use hi pressure systems where I'm located.
    So my question is, on the high pressure type systems does the pipe have to be welded ?

  14. #13
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    May 2004
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    Salt Lake City/Tooele
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    So what is that click noise you hear 30 seconds to a minute after initial ignition that coincides with the furnace glitching??? You say it is on the "controller".

    Does the furnace trip out EVERY SINGLE TIME you hear this click?? Or is it just every once in a while?? You make it sound like the click you hear has a direct relationship to the gas valve dropping out??

    I got a sneaking suspicion that the click you are hearing is the control board mounted blower relay turning on 35 seconds delay after ignition. If the gas valve is being affected every time after this relay is being energized, then I would assume there is a voltage drop dramatic enough to affect the either the gas valve's coil and cause it to drop out or affecting the board itself. The board is also energizing the EAC and Humidifier at the same time per the timing diagram I attached below.
    Attached Images Attached Images  

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