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  1. #1

    Goodman tripping rollout limit switch

    Good morning all, Im having some trouble with my one year old Goodman GMVC95 variable speed, condensing furnace. Sorry in advance for my drawn out description, but here is the background info:

    This furnace worked fine for the last year, my troubles started this year. The manual reset rollout limit (upper left one) on the back wall of the upper compartment frequently trips open. It also gives an error code of four blinking red lights, which apparently normally means a blocked air filter.

    I called in the installer, who thoroughly looked things over and we found the following things out. The switch trips primarily when the furnace is required to kick into the high cycle (after ten minutes of runtime without meeting temperature). The unit will run fine for days, provided that the temperature setting is fairly constant, and it never needs to kick into high. We checked the switch itself (and also swapped it with others in the furnace and determined the switch is good. He also checked gas pressure, and determined it was within the correct range. There is no noticeable flame rollout that occurs to trip the switch. There was also no blockage in the intake or exhaust pipes on the furnace which may limit combustion air flow. With the furnace door left off, the switch will not trip at all (which makes me think its a temperature issue, but not a true rollout).

    The furnace will also not trip the limit with the furnace door closed, and the furnace filter removed. I had reinstalled a new 'better' MIRV 11 ( I think) filter in the fall which was a lot denser than the filter used the previous winter. My installer replaced the filter with a very inexpensive one which seemed to solve the problem. We concluded that the new, dense filter was restricting air flow enough on the high heat cycle, and causing an overheat issue in the furnace. It seemed to solve the problem, and he left. Since this wasnt a warranty-able issue, I was forced to eat the bill for his time.

    Everything worked fine for about a week, and then the same problem started to reoccur, even with the crummy filter. Im reluctant to immediately call him back until Ive exhausted all my options, since Ill likely again have to pay for this visit again if he cant find a legit furnace issue.

    Ive determined that the problem will not occur if I pull out the filter a slight amount. This seems to allow better airflow through the furnace and will not trip the rollout. Obviously I cant leave the filter out, so I sought to determine if I was not getting enough airflow due to a cold air return problem, or a heated air problem. I inspected the air conditioning condenser coil, and found it to be completely clean. While I had open access, I allowed heated air to vent out my access hatch, prior to the air conditioning condenser. The rollout switch still tripped without any heated side limitation, so I determined it must be on the cold air side.

    I needed a cold air return in my basement, so I installed one (according to code, far away from furnace, etc). I thought this might help if there was too little cold air return flow, however his did not help. This is about where I stand. My next step will be to create an access just a foot or two away from the filter on the cold air side, to be sure that there is no cold air return air flow problem. Im not terribly confident that this will solve anything.

    My wife is due to have a baby any day, and Im very concerned that even after being away from the house for a day or two we'll return to no heat whatsoever. This switch does not reset automatically, so once it goes it needs to be manually reset.

    Please let me know of any thoughts on this issue.

    Thanks for taking the time to think on this,

    -Dave

  2. #2
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    Flame rollout usually indicates a problem with combustion or venting, possibly a restriction in the vent pipe, or something improper with the draft inducer.

    You should have your hvac tech look into this. There's definitely a problem.

  3. #3
    Join Date
    Sep 2006
    Location
    Montana
    Posts
    983
    My guess is that there is something wrong with the venting of the furnace. It may be an obstruction in the intake or the wrong sized pipe. What size is the pvc venting and how long is it? How many 90's are there in the venting? Is it within the manufactuers specs for venting lengths? These are all things the tech should be looking at. If the furnace runs with the burner box door off, there's a combusiton air issue. If the tech was just out there recently(within the last couple of months or sooner), you shouldn't have to pay him for the service call again. You already paid him to fix it, he evidentally didn't, so now it's on his dime, IMO.

  4. #4
    Join Date
    Oct 2006
    Location
    The Beach
    Posts
    701
    I would have the tech check that vent piping again. A slight restricken (Water)will cause this problem. Or not graded right. The roll out is doing its job. Something is wrong. He did check the gas pressure?

    Merry Christmas
    Blue Fox

  5. #5
    The tech did check the gas pressure and noted that it was within specs. The venting pipe goes out of the furnace for about a foot, then a 90 degree elbow, followed by about a ten foot horizontal run, an upward turning 90, one foot up again with an elbow that goes out the wall. So all in all Id saw three elbows (not counting the one outside the house to keep rain/snow out, plus 12 to 13 feet of straight pipe. The outside diameter of the pipe is about 2 and a half inches, so Im guessing its 2 inch pipe or so.

    Ill try to look up the specs for this and see what is required.

    I do have a condensate pump, rather than a straight drain. Ive heard the pump running so I assumed it was working. Would a backed up pump cause a similar issue?

  6. #6
    Join Date
    Jun 2008
    Location
    Cincinnati, Ohio
    Posts
    2,176
    Quote Originally Posted by Splash View Post
    The tech did check the gas pressure and noted that it was within specs. The venting pipe goes out of the furnace for about a foot, then a 90 degree elbow, followed by about a ten foot horizontal run, an upward turning 90, one foot up again with an elbow that goes out the wall. So all in all Id saw three elbows (not counting the one outside the house to keep rain/snow out, plus 12 to 13 feet of straight pipe. The outside diameter of the pipe is about 2 and a half inches, so Im guessing its 2 inch pipe or so.

    Ill try to look up the specs for this and see what is required.
    2" is probably required, but IMO, 3" is the only way to go. You eliminate a lot of potential problems by running the vent in 3".

    Quote Originally Posted by Splash View Post
    I do have a condensate pump, rather than a straight drain. Ive heard the pump running so I assumed it was working. Would a backed up pump cause a similar issue?
    Possibly, but the more logical answer is that the pressure switch(es) would never close due to condensate backing up in the collector box of the secondary HX.

  7. #7
    Join Date
    Dec 2010
    Location
    Chillicothe, Ohio
    Posts
    19
    The part that raises a question to me is that you said it worked fine the first year. From what you've said, I'm suspecting an air flow issue. If your filter wasnt properly installed initially, then the first year of operation would be about long enough to get that secondary heat exchanger good & plugged, which could cause an over temperature situation. Either way, it's something that should be checked by a qualified tech.

  8. #8
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    yeah call the guys and explain. The you-put-in-a-tight-filter thing sure looked good untill it acted up again. some of us might at least come out and look again on our dime.

  9. #9
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    Call him back, and tell him it's still not fixed. Also tell him to have a refund ready for the last non-warrantable call.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  10. #10
    Join Date
    Apr 2002
    Posts
    1,383
    I agree this is likely to be a venting related problem.


    My suggestion is that you need a way to analyze what's going on with the venting system, and the way to do that is to install a monometer to measure the pressure in the venting system.

    Ideally you'd find out the acceptable range of pressures for the system and compare that to what you have. Another approach is to switch the furnace input on high and observe what's happening to the pressure as the length of the run causes the rollout switch to trip.

    Another issue to test is the point at which the pressure switch opens. Is it opening when it should, which probably ought to be before the flame rollout switch trips?


    As an example of what you might find with this approach, I have to relate one of my heroic diagnostic coups with a Carrier AAW condensing furnace, vented through the roof.

    The pressure switch was opening after about 15 minutes of burner operation. If you turned the power switch on and off, everything would go back to normal for another 15 minutes.

    What I found when I put a manometer on the system was that the pressure was normal in the beginning, but gradually became marginal until the pressure switch opened.

    Can you identify what was causing this problem?

    (Answer below).




























    Water droplets began condensing in the vertical vent pipe and were suspended by the air flow through the vent pipe. Eventually the water droplets got big enough to obstruct the air flow enough to cause the pressure switch to open. Turning the power off allowed the water droplets to drain down into the furnace.

    Solution: a larger sized PVC vent pipe.

  11. #11
    This afternoon the issue got even worse. The furnace will now sometimes trip off before even reaching the high heat output level. I disconnected the intake vent to allow ambient room air to be used as combustion air, and the problem persists. I also disassembled a portion of the exhaust vent to be sure there was no blockage, and there was not. I checked the exhaust specs and found that with my pipe run I would be allowed 8 elbows, my setup only uses 4.

    My old solution of partially pulling out the filter also doesn't work all the time anymore. The only thing I've noticed that for sure prevents the tripping is running without the door on.

    The installer is returning tomorrow. He mentioned for sure checking the secondary heat exchanger, and also turning down the gas pressure to the low end of spec. I'll be sure to to mention an exhaust pressure check.

    Frustrating!
    Last edited by Splash; 12-15-2010 at 06:07 PM. Reason: Typo

  12. #12
    Join Date
    Nov 2010
    Location
    Andover Kansas
    Posts
    2,115
    Quote Originally Posted by Splash View Post
    This afternoon the issue got even worse. The furnace will now sometimes trip off before even reaching the high heat output level. I disconnected the intake vent to allow ambient room air to be used as combustion air, and the problem persists. I also disassembled a portion of the exhaust vent to be sure there was no blockage, and there was not. I checked the exhaust specs and found that with my pipe run I would be allowed 8 elbows, my setup only uses 4.

    My old solution of partially pulling out the filter also doesn't work all the time anymore. The only thing I've noticed that for sure prevents the tripping is running without the door on.

    The installer is returning tomorrow. He mentioned for sure checking the secondary heat exchanger, and also turning down the gas pressure to the low end of spec. I'll be sure to to mention an exhaust pressure check.

    Frustrating!

    Every furnace on the data plate tells a "Temp rise" range that the furnace should fall between. Ask the tech to see what the temp rise is on your furnace with the filter in and with it out. If it is still high with the filter out, then it could be too high gas psi, too low blower speed, not enough ductwork, a dirty a-coil..etc, etc...an experienced tech will know how to determine the issue or issues.
    .


    The statement below is my signature and just my overall feeling towards our industry and does not necessarily pertain to you nor this thread.


    There really isn't a legitimate excuse for not doing the job correctly!

  13. #13
    Join Date
    Nov 2010
    Location
    Andover Kansas
    Posts
    2,115
    If the temp rise is in line, then I agree with those who have posted about venting or secondary exchanger issues.
    .


    The statement below is my signature and just my overall feeling towards our industry and does not necessarily pertain to you nor this thread.


    There really isn't a legitimate excuse for not doing the job correctly!

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