# Burner flame sputters



## qbert (Mar 23, 2009)

If it was the valve it would do that regardless of the blower.


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## hvac5646 (May 1, 2011)

sputtering? Are the burners extinguishing and relighting?


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## ben's plumbing (Oct 6, 2011)

seem to me if you start having and unstable flame on burner after blower starts....I would think you have a problem with heat exchanger....ben


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## Tabb (Jan 19, 2009)

qbert said:


> If it was the valve it would do that regardless of the blower.


That would make the most sense but the guy that said the gas valve was faulty seemed to think that the blower wasn't an issue. He came recommended by a co-worker.

No the flame is not getting extingished. They aren't even changing color, still a nice blue color. But when the fan comes on, the flame starts to dance.

There are 3 burners, it only appears as though the one on the right is affected. The one farthest to the left seems unchanged, the middle one changes a tiny bit, but right one dances the most and the sputtering seems to be coming from the right.


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## ben's plumbing (Oct 6, 2011)

Tabb said:


> That would make the most sense but the guy that said the gas valve was faulty seemed to think that the blower wasn't an issue. He came recommended by a co-worker.
> 
> No the flame is not getting extingished. They aren't even changing color, still a nice blue color. But when the fan comes on, the flame starts to dance.


 only thing that can cause that is air from blower....has to come through exchanger..... have it check asap


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## yuri (Nov 29, 2008)

The older Wav's and Cav's are known to crack on the dimples of the heat exchanger. Sounds like yours is cracked. Need an experienced Carrier or Bryant or Payne tech to know where to look if possible. All 3 of those brands are Carrier and look the same inside.


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## Tabb (Jan 19, 2009)

I know stuff happens but is it common for a 7 year old Carrier heat exchanger to crack?


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## Doc Holliday (Mar 12, 2011)

Have you ever had furnace overheating issues?


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## Tabb (Jan 19, 2009)

Doc Holliday said:


> Have you ever had furnace overheating issues?


Not that I know of......We usually run it around 21 deg c. Its setback during working hours only, 19 deg c. Blower is set cycle 3-4 times / hour. And we live in Vancovuer where winters are very moderate.

If the heat exchanger is leaking, its going to be a min of 3 weeks before it gets repaired. The tech said at least2-3 weeks to get the part in....and then its 4-6 hours to replace. Does that sound about right? The furnace is in a bit of a tight spot.


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## Doc Holliday (Mar 12, 2011)

I live in what is called the HVAC capitol of the world, for the most part getting any part for any make and model takes me less than a thirty minute drive.

The time it takes to do the job sounds about right.

What I was getting at if you had furnace overheating issues would be to have the duct work looked at, possibly adding a return air as restricted air flow would be the factor in this cracked heat exchanger.

Keep those filters clean, new.


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## yuri (Nov 29, 2008)

If it has poor airflow issues or was overfired due to high gas pressure in the burner it can crack prematurely. Not sure if they changed the metallurgy in the newer models but the older ones had some problems. They are a huge pain to change the cells as the heat exchanger comes in 3-4 cells/pieces and can be time consuming so he is right (unless they changed that recently). Not sure why it would take that long to get the parts but most manufacturers are going with this BS "lean stocking" "low overhead" business model.:furious:


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## Tabb (Jan 19, 2009)

Doc Holliday said:


> What I was getting at if you had furnace overheating issues would be to have the duct work looked at, possibly adding a return air as restricted air flow would be the factor in this cracked heat exchanger.
> 
> Keep those filters clean, new.


Crap. You mentioned restricted air flow. We started using high performance air filters last year. Our thermostat keeps track of the days of use and I change them out when the counter reads 30 days, usually works out to be every 2-3 months. Think this may have cause some overheat issues?


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## yuri (Nov 29, 2008)

YES. Those units have a low 170 deg F limit control setting on the ones I have seen and don't like overheating (along with other brands). Reread my post above yours.


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## Doc Holliday (Mar 12, 2011)

Yes. There's another thread going on here in the hvac section right now concerning pressure drop across certain filters. 
http://www.diychatroom.com/f17/lennox-ml193-filtrete-129302/

Usually these high performance, thicker filters restrict air flow and cause the motors to run hotter as there's less, well harder to get, air for them to attempt to pull.

I personally only use the cheapest and thinnest, most generic Wal-Mart filters at my place. I change them every three weeks regardless.


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## beenthere (Oct 11, 2008)

If you don't think it has anything to do with the blower being on. If you also have central A/C on that furnace. At the thermostat, turn the fan switch to on. Then turn the heat setting up so the burner comes on. Watch it light, and watch the flame.


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## yuri (Nov 29, 2008)

merv 7 or 8 is what I would use with that furnace. get a temp rise test done and manifold gas pressure/firing rate checked also.


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## Doc Holliday (Mar 12, 2011)

But don't let it run for too long. A crack in the heat exchanger means CO is leaking somewhere as well. You won't smell it yet you won't wake up, ever.

Do not use the furnace until it's repaired, not even for a few minutes. It can be lethal.

No joke. No matter how cold it gets, if icycles are forming on your eyebrows while in bed for the night, do not turn it on.


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## Tabb (Jan 19, 2009)

Thanks for the replies guys!. We've got enough space heaters for the kids and our bedrooms and the kitchen has got an electric radiant heated floor. I guess we'll have to bundle up for 3 weeks. LOL.....I recently changed our electricity billing to equal payments. Guess they'll be making some adjustments to my bill next year.

Thankfully the problem was caught in time. None of the CO detectors went off or registered anything, our 2 and 4 year old boys sleep on a different floor than us....


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## Tabb (Jan 19, 2009)

OK...one final question. Is there anything else, other than a cracked heat exchanger, that could cause the burner flame to change when the blower turns on?


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## yuri (Nov 29, 2008)

No. As long as you have a constant manifold gas pressure the flame should not sputter and the tech should check that and too see it is not overfired. In some bizarre scenario the voltage to the gas valve could be fluctuating due to the fan shorting the circuit board but I have never seen that in 33 yrs or doubt it could ever happen. I would check the gas pressure and voltage to the valve to make sure it is constant. Post a vid of it on U Tube so we can hear and see what it is doing. Make sure the blower fan is NOT sucking any air out of the furnace room with any vents in the return duct open to the furnace room (rare but it happens). That could interfere with the flame but it would not happen after 7 yrs all of a sudden.


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## Tabb (Jan 19, 2009)

I posted the youtube vid as requested.
http://www.youtube.com/watch?v=PcjeykRlqE8&feature=youtu.be


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## Doc Holliday (Mar 12, 2011)

almost like a weld on the exchanger broke. That crack is pretty significant.


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## yuri (Nov 29, 2008)

That is a BAD scenario and I would not use that furnace anymore. Used to be called a CTA that model and I have seen lots of them and none of them did that. Definitely a cracked heat exchanger cell IMO.


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## Tabb (Jan 19, 2009)

Turned off the furnace last night. Just turned it on long enough to make the video.

I called Carrier this morning to ask why it would take 2-3 weeks for my repair guy to get his hands on a replacement part, in the middle of winter!! Spoke to 3 people before I got a call back from the DSM. Turns out there is an exhanger in Sasketoon and it can be here within 24hrs. 

I've got a tenative appointment for Thursday Morning to get the repairs done.


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## Doc Holliday (Mar 12, 2011)

Awesome news. Please take pictures or video of the crack and post it here. I'd like to see it.


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## ben's plumbing (Oct 6, 2011)

Tabb said:


> I know stuff happens but is it common for a 7 year old Carrier heat exchanger to crack?


 I have had heat exchangers crack after a couple of months....its man made ....


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## Tabb (Jan 19, 2009)

So....the tech has just removed the exhanger. There appears to be 3 exchanger plates (1 for each burner) held toegther by some brackets. There are no visable signs of leakage on any of the heat exchanger plates. No signs of soot, discoloration, rivets and crimps all seem intact. Unless something is happening tothe metal when it heats up, the exchanger looks visually ok.

Guess I'll see when he fires it back up


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## beenthere (Oct 11, 2008)

Fired up yet?


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## Doc Holliday (Mar 12, 2011)

Pics?


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## Tabb (Jan 19, 2009)

Sorry for the delay, things have been a little busy. And sorry, no pics. 

Anyways, looks like replacing the heat exchanger worked. The burner no longer sputters. However, the tech thinks the exchanger may have been plugged and not leaking. 

When he was removing the exhaust pipe between the furnace and chimney liner, he found some debris that he said was due to corrision in the liner. He said the liner may be too large of a diameter for the size of furnace and rise of my house. A 6" liner was installed but it should have been a 4" liner. 66000btu + approx 40 ft rise.

Where the exhaust is located on the furnace, any debris from the pipe would fall into the left most exhanger chamber 1st. Comments?


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## hvac5646 (May 1, 2011)

for the size of furnace a six inch liner is over kill.. even at a height of forty feet.

With out looking at the chart I would say a four inch liner for sure with insulation sleeve around exterior of line or a five inch.


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## Missouri Bound (Apr 9, 2011)

Glad you got it fixed...and get a CO detector.


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## yuri (Nov 29, 2008)

It was definitely leaking. Bad weld/crimp joint or whatever they use which opened up from heating and expansion. It was DIRECTLY related to the fan coming on and air pressure so a blockage would not cause a problem as it would do it when the fan was off. There is a pressure switch to stop the burner if the chimney is blocked or from blockages so that was not the problem. Having seen that type of flame many times from cracked heat exchangers I could tell. Blockages give you a slow buildup of gases and slow flame rollout out the front of the burners. Your flame problem happened quickly and at the exact time the fan started. Debris cannot get into the heat ex as it gets stuck in the exhaust fan first.


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## Tabb (Jan 19, 2009)

:yes


yuri said:


> It was definitely leaking. Bad weld/crimp joint or whatever they use which opened up from heating and expansion. It was DIRECTLY related to the fan coming on and air pressure so a blockage would not cause a problem as it would do it when the fan was off. There is a pressure switch to stop the burner if the chimney is blocked or from blockages so that was not the problem. Having seen that type of flame many times from cracked heat exchangers I could tell. Blockages give you a slow buildup of gases and slow flame rollout out the front of the burners. Your flame problem happened quickly and at the exact time the fan started. Debris cannot get into the heat ex as it gets stuck in the exhaust fan first.


that's good to know. The exchanger is crimped at the edge and riveted in the center. There were some dark Grey discolored areas in several different spots on all 3s
exchangers. The rest of it was a normal stainless color. 

Do you think the corrosion and oversized liner is something I should deal with or leave alone?


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## yuri (Nov 29, 2008)

If the chimney goes thru the middle of the house and stays warm it should be OK. If it goes thru an exterior wall and can get cold then that is a huge problem as condensation can occur. Then it should be downsized and replaced with a B vent ( pipe within a pipe ) type liner/vent to meet the code.


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## Tabb (Jan 19, 2009)

Thanks Yuri. Yes the Chimney is in the center of the house. The last 5 feet of the liner is exposed but is encased in a steel liner covered with vent cap.

About 6 years ago, after the furnace and liner install, we had some chimney work done. The exterior of the brick was re-pointed and a cenement cap was placed over the chimney for asthetic purposes. Unknown to us at the time, the mansonary guys cut the liner vent cap and squashed it down to fit the cement cap on. There were still exhaust openings but the cap basically lost 50% of its venting area. Could this have caused excessive condensation in the liner? The brick chimney was removed approx 5 years ago when our roof was done. I'll try and dig up some old pictures.


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## hvac5646 (May 1, 2011)

yep. it could have.


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## yuri (Nov 29, 2008)

If it worked OK for 6 yrs then it should not have caused your heat exchanger problems or any condensation. However it should not have 50% of its area reduced and that does not meet the code and can cause pressure switch tripping problems or tripping of the spill switch etc. Sounds to me like you should get a proper 4" B vent installed for the safety of your family and to meet the code irregardless of the aesthetics. Make sure they size it properly taking into account the horz run from furnace to chimney and look it up in the code book. Should also have B vent from the furnace to the chimney.


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