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 Repairing / Servicing Lennox Gas Furnaces
 G20Q3/4E-100-3 Audible boom when burner lights?
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schenken

8 Posts

Posted - 02/17/2007 :  10:26:50 AM  Show Profile  Reply with Quote
I have a G20Q3/4E-100-3 furnace just off our famly room in the lower level of my house, manufactured in 1993. This time of the year the furnace runs quite often due to the sub zero temps. This morning at 2:30 AM I was awoken by an audible boom followed within 5-10 seconds by another audible boom which shook the house. Then silence except for the furnace coming on. I've not heard an audible boom again since this morning. My wife has heard the same audible boom earlier in the week twice but was unable to locate a source. We had the furnace serviced and checked for the winter this past October and the service man found nothing wrong during his once over. I took the covers off the furnace this morning later in the AM and saw nothing jarred , cracked or out of place. Just the same we're scheduling a HVAC service call Monday. Could this furnace ever come on with an audible boom?

Cozy.Support

5709 Posts

Posted - 02/17/2007 :  10:33:10 AM  Show Profile  Reply with Quote
We have to break this down to two possibilities:

First scenario:
Delayed ignition. Since you have electronic ignition, the most likely cause would be dirty burners or restrictions in the heat exchanger. Since you know you have had the service serviced, and nothing was found, along with the fact that you have no apparent signs of flame roll out or bad delayed ignition (like the access panel being blown off) it appears that this is probably not the likely source of the noise. However, if you have any doubts at all, you should have the furnace checked again.

Second scenario:
More likely in my estimation, is that you have a duct that is popping when it expands. This phenomena is called "oil canning" which relates to the pop you get when you push in on the bottom of the old funnel shaped oil cans (not many of them around any more). While not dangerous, it can certainly be annoying.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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Cozy.Support

5709 Posts

Posted - 02/17/2007 :  10:41:07 AM  Show Profile  Reply with Quote
One more possibility. If this noise is happening just as the blower is coming on, check for broken/loose hub on the blower wheel. Also, check for loose or brokent blower motor mounts.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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schenken

8 Posts

Posted - 02/17/2007 :  10:46:12 AM  Show Profile  Reply with Quote
Thanks for your reply. We've lived in this house for nine years and this is the first time I can recall this happening. I can take a look at the blower for a broken/loose hub.
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schenken

8 Posts

Posted - 02/17/2007 :  10:48:48 AM  Show Profile  Reply with Quote
I took a look at the blower hub, it's tight, no looseness.
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Cozy.Support

5709 Posts

Posted - 02/17/2007 :  10:55:00 AM  Show Profile  Reply with Quote
If the hub is broke loose from center divider in the wheel, it may not be easy to determine. But if it is, sometimes the hub will spin on the divider, and make quite a bit of noise. Another thing than can cause it is if the mount is broke, the centrifugal force of the motor starting up can cause the blower wheel to swing over into the blower housing, making a lot of nose, and then after the starting forces dissipate, the blower wheel re-aligns itself, and stops hitting the housing... just things to look for.

After re-reading your post, the 10 second rumble really doesn't go with delayed ignition nor oil canning. That sounds more like a blower issue.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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schenken

8 Posts

Posted - 02/17/2007 :  11:07:35 AM  Show Profile  Reply with Quote
Thanks for your replies. The furnace has been coming on all day with it's normal noises. Flow of gas, ignition, and after 15-20 seconds the blower kicks on. So far so good, it's cold outside, and I want the furnace to keep working.
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Cozy.Support

5709 Posts

Posted - 02/17/2007 :  2:19:03 PM  Show Profile  Reply with Quote
Good luck. If your service tech finds the issue, please let us know what it was.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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MechAcc

1499 Posts

Posted - 02/19/2007 :  8:21:04 PM  Show Profile  Reply with Quote
Does the furnace operate on Natural or Propane gas?

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have them test the undiluted combustion gases for proper combustion and carbon monoxide production.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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shoe

141 Posts

Posted - 02/25/2007 :  11:42:20 AM  Show Profile  Reply with Quote
"This time of the year the furnace runs quite often due to the sub zero temps. This morning at 2:30 AM I was awoken by an audible boom followed within 5-10 seconds by another audible boom"

Do you turn down your thermostat at night (or use temperature setback on an electronic stat)? This could be significant in that the problem only happens after an extended 'off' cycle.

Most booming noises are of the mechanical or 'oil-can' variety, and the vast likelihood is that you are experiencing one of them. If, on the other hand, the booming sounds like a gunshot, followed by another gunshot, you possibly have delayed ignition.

My comments will only cover the delayed ignition possibility, the more likely causes have been covered nicely here.

Lennox issued a service bulletin 8 or 9 or 10 years ago affecting some G20s that had experienced misalignment or deformation of the heat exchanger which led to delayed ignition. I tend to think that this is not the problem you're experiencing because in that case the delayed ignition was very 'reliable'; it happened most of the time. The service bulletin described a method for measuring certain dimensions on the heat exchanger (which requires removing the A/C coil in most instances), and I think Lennox has (since then) come up with some sort of gauge to make the measuring easier (though I've never actually seen one). Virtually all the affected furnaces have long since gotten new heat exchangers.

I have on the other hand experienced *exactly* what you describe, once. On a G20.

To make a (very) long story short, everything that could even possibly matter had been replaced on this furnace, and the problem still remained. It was finally 'cured' by adding butterfly air valves (for a G8 or G10 model) to the front of the burners so that burner primary air openings could be closed off about three-quarters. I don't know about you, but I get a bit more than a little quesy about altering the combustion-related aspects of a furnace - in essence when one does so, they are becoming the manufacturer of the furnace and assuming all related liability for it. The contractor I was working for ended up making the homeowner a deal she couldn't refuse on a new G60 - so much time had been invested & the homeowner had become uncomfortable enough with the permanency & efficacy of the 'solution' it just made sense.

Basically the cooler (and denser) combustion air in the stone cold furnace rendered the fuel too lean to ignite smoothly. Once it had gone through its 'bang' or 'bang-wait-bang', the furnace was warm enough to ignite properly thereafter. Or something. We never did find out. This one's for Agent Mulder.

So to help the technician tomorrow with isolating the nature of your noise, I recommend this:

Turn the furnace off (at the thermostat) for several (four +) hours before they arrive.

When they arrive, DO NOT let them touch the thermostat. Bring them to the furnace and explain the symptom. Have him or her remove the front cover of the furnace to observe the first light-off, but do not allow them to sit/kneel directly in front of it (or where they might injure themselves reacting to an explosive flash-bang).

YOU go to the thermostat to turn the system on. They'll know when you have (the burner damper door opens prior to ignition).

If you're experiencing this sort of problem and there is no obvious reason, I don't know what to recommend. One alters a furnace at their own peril (and too frequently other people's peril).

"There's nothing going on here that a new G60 wouldn't fix".

Hope that it's oil-canning.

-------------------------------------------

I am not affiliated with Cozy Parts or Lennox in any way.

The opinions I provide are my own. You have no idea whether or not I'm qualified to hold them. Use them at your own risk.
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schenken

8 Posts

Posted - 03/05/2007 :  08:03:28 AM  Show Profile  Reply with Quote
Thanks for the replies. I have a gas furnace with an electronic thermostat, it's set back to 64 for the evening and most of the day once the kids have gone off to school. I doubt it's "oil canning" The noise and vibration is way to loud and forceful.
It's been quiet up until this morning. It's been almost two weeks with no problems with the furnace lighting up. This morning while I was getting ready to go to work and while brushing my teeth at 4:30 AM there was a loud boom which distinctly came from under the floor of the bathroom I was in which sits over the furnace room. I felt the floor shake. Immediately after wards the furnace blower came on. Kinda freaked me out. I went down to the furnace room. When I first opened the door and went in I smelled something odd, that's hard to describe. Unburnt gas/air mixture? It was not the usual smell I associate with that room. I shut off the furnace and removed the covers and saw nothing amiss. After putting the covers back and switching it back on, it lit as it normally does. What would you guys do if this happened to you? If I call my HVAC guy how do I explain what happen with out sounding whacko? What should he look for? I wonder if there’s some way I can make this happen deliberately as the last posting suggested.
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Cozy.Support

5709 Posts

Posted - 03/05/2007 :  8:14:04 PM  Show Profile  Reply with Quote
Just tell him the truth. Did the HVAC tech come out a few weeks ago? I wouldn't mess around with it. You need to get it looked at ASAP.



Cozy.Support does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx

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MechAcc

1499 Posts

Posted - 03/06/2007 :  06:31:14 AM  Show Profile  Reply with Quote
Is the furnace operating on Natural Gas or on LPG (Propane Gas)?

Delayed ignition is usually from burner misalignment. Crossovers dirty or something that may not always be apparent, debris in the burner manifold. The debris will sometimes float up to the burner orifice restricting or blocking gas flow. It is best that the technician remove the burners and burner manifold. Clean the the burners and the light over bars with a piece of sheet metal to slide through the slots. Blow all the burners and burner crossovers with compressed air. Remove the gas valve and the burner orifices from the manifold. Run a length of flexible wire into the manifold all the way to its end. This will break loose any spider web that may have been built. Blow it out with compressed air and inspect carefully. Inspect the orifices for any deformities. Reassemble. the burner light over bars on the G20 have metal clips that slide over the two adjoining bars to keep them aligned.

Then have the technician insert the probe of a co/combustion analyzer in the outlet of the far left chamber in the draft hood. Observe the meter from burner start up to blower on to furnace off. Then after shutdown move the probe to the next chamber. Test each chamber through an entire light off to shut down. CO levels over 400ppm at start up in any chamber indicates a light off problem. CO levels normally are around 50 ppm or less. If the CO or oxygen levels climb when the blower comes on there is a crack or hole in the heat exchanger.

Have the spark wire inspected carefully. If it shows signs of drying or overheating replace it. Depending upon the pilot burner this may also require replacing the pilot burner as some wires are molded into the porcelain. Make sure that the rubber grommet for the spark wire is in good condition. If it is falling apart or missing replace it. The spark wire may be shorting to the metal case. This removes the spark at the pilot. Gas could build up and then a spark is then established at the pilot burner. This spark wire shorting is something that has happened to me so I know what I am talking about.


Another possibility is that with anything electrical is that the ignition control may be energizing the pilot burner and main burner terminal when there is a call for heat. This would allow large amounts of raw gas to be dumped into the chamber before a pilot is proved.

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have them test the undiluted combustion gases for proper combustion and carbon monoxide production.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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schenken

8 Posts

Posted - 03/09/2007 :  08:18:13 AM  Show Profile  Reply with Quote
Thanks for your input. We experinced delayed ignition two more times within the last three days, very intermittent. We have a service guy coming over this AM. He's from our regular HVAC company we have used for the past nine years or so. I'll let you know what he does or doesn't find.
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schenken

8 Posts

Posted - 03/09/2007 :  11:36:08 AM  Show Profile  Reply with Quote
We had a service guy out this morning. He took apart the pilot light valve and cleaned/reassembled it. He also checked the fit with all the spade(stake on) terminals. He found a loose one on the ignition module. He cycled the furnace a dozen times before doing anything and it lit propoerly. He cycled it a dozen times afterwards and it lit normally every time. So for now that's all that was done. If it lights loudly with a delayed ignition in the future he suggest that the ignition module be changed.
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gerardm

1 Posts

Posted - 03/12/2007 :  11:04:53 PM  Show Profile  Reply with Quote
Having the same problem as schenken. I've noticed that it happens(BOOM LIGHT) after the G20 has been off for several hours and cold soaked(?).I use a setback thermostat so the BOOM occurs in the middle of the night/early AM. We have had the tech out here 3x's andit finally was observed by him. He had no idea why it happens. Every time that I've been awaken by the BOOM there is an excess of Natural Gas(smell) in the area, maybe ignition is delayed too long? Shouldn't the igniter go before the gas valve inputs/opens to let gas in ?? The tech said he might have to replace the GAS valve --possible? All of this has been happening since the BLOWER was replaced- any tie in to this ?? Thanks
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