Furnace - Slight Delayed Ignition

Discussion in 'HVAC Heating & Cooling' started by Jeff_08, Apr 7, 2008.

  1. Jeff_08

    Jeff_08 New Member

    Messages:
    34
    Location:
    Chicago area
    I have an American Standard gas furnace (approx 10 yrs. old) that has a slight case of delayed ignition lately. I have only removed the flame sensor to scuff off the buildup and brushed dust out of the burners (after removing them), but those are the only parts I have touched and after putting the burners back it seems there is a slight delayed ignition which causes a sound as the gas ignites. I know this is probably not a normal function but everything was put back exactly as it was before removal so I don't know what else could be causing this issue. I've read about it as much as I could find but mostly old burners are mentioned as the cause and that replacement would fix the problem. This didn't exist before I took them out and cleaned the dust but I thought maybe someone would have some suggestions. The burners look fine as far as I can tell, the HXs don't appear to have any cracks, and the filter is changed regularly. Anything else I can check (with a meter, etc.) to figure this out? Thanks for any help.
  2. tommyboy

    tommyboy New Member

    Messages:
    2
    How is the burner alignment and the cross over?Did you look at the orifices to see if you have a spider egg sac in one of them.
  3. gizza job

    gizza job Plumber

    Messages:
    12
    Location:
    Barrie, ontario
    have you cleaned the pilot light and main burner jets? its quite possible you may have partially blocked them with lint, or has the spark electrode been knocked out of line?
  4. Jeff_08

    Jeff_08 New Member

    Messages:
    34
    Location:
    Chicago area
    I forgot to mention, it doesn't have a pilot but it has the glow bar ignitor. The ignitor looks fine to me and is being supplied the proper voltage as far as I could tell. The burner alignment and crossover I'm not positive about - when you put the burners back in there are slots to make sure they end up in the same spot they came from. Crossover I don't know exactly how that works with my furnace. It has 5 burners which look like tapered tubes and there don't appear to be any areas that "connect" each of them, or maybe I'm just confused as to what crossover is. When I brushed them out, I didn't see anything blocking the flow which is what I was attempting to clean out. After cleaning it's the third, fourth, and fifth burners from the ignitor that have the problem. It makes a popping sound due to the delay in igniting. I can't seem to find anything visually that seems to be causing the problem. The only thing I can't check is the gas manifold because it's not easily removed and I don't want to mess with that. The holes in it don't have any blockage.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,303
    Location:
    Cave Creek, Arizona
    ignition

    If the ignitor is working on one of the first burners, there will be a delay as the flame is passed from burner to burner as they receive a supply of gas to ignite.
  6. Jeff_08

    Jeff_08 New Member

    Messages:
    34
    Location:
    Chicago area
    The delay appears to be between the second and third burner (from the ignitor end) and it makes a pop sound when the last 3 ignite...just doesn't seem normal. When I looked it up it sounded like this is called a delayed ignition and some people report it sounding like a gunshot which mine has the popping sound. There aren't any flames shooting out of the burner area or anything crazy like that but it was something that I'd call abnormal without knowing what the cause is.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,303
    Location:
    Cave Creek, Arizona
    pop

    Ignition is not instanteous or simultaneous across the burners. If there is no pilot light to light those burners they will flow gas until the intermediate burners ignite and pass the flame across to the last ones. At that point the "accumulated" gas will ignite with a bang or a pop and light the burners.
  8. Jeff_08

    Jeff_08 New Member

    Messages:
    34
    Location:
    Chicago area
    Ok, I see. It's just the sound isn't consistent and is sometimes loud enough to wonder why it's loud enough to hear from the floor above where the furnace is. It's not often that happens but it does on a regular basis.
  9. wraujr

    wraujr Member

    Messages:
    57
    Location:
    MD
    Clean crossover

    Sure sounds like the flame is not crossing over from burner to burner. Eventually enough gas builds up and you basically get a small explosion (hence the pop sound). Now since you don't mention a crossover tube, I suspect you have burners like mine. They actually remind me of a single-engine jet fighter (i.e. a round tube with wings). If thats the case, the "wings" function as the crossover path. There are small dimples that keep the upper and lower sheet metal separated enough for a small flow of gas and the edges of the "wings" should be slightly flared. The flame moves along this edge from burner to burner.

    The small gap builds up soot/debris and can get clogged. The best way to clean is remove, wire brush, and blow with compressed air....

    Or try this, while furnace is running observe if there is a small continuous flame on the crossover. (it will always be there when running, unless clogged). Now ever so LIGHTLY tap the "wings" edge with a screwdriver and see if debris comes out. It will glow yellow, not blue like the flame. See if this gives you a more continuous crossover flame. Worked for me two weeks ago.
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