My furnace has developed a new issue. The flame on one of the three burners on my 25 year old Carried super saver gas furnace comes all the way out to the gas nozzle on ignition of the burners. Then, it appears to burn normal blue color. Cracked heat exchanger?

 

I'm really not understanding what you're saying?

Are all the other burners lighting and one of them delayed ?

 

If it behaves that way only when the blower first starts up -yes, it be a cracked heat exchanger.

But if it does that before the blower (that blows hot air out your registers), comes on, - then it sounds like the burner needs cleaning, and possibly that section of heat exchanger above it is badly sooted up. Ever notice if compard to the other burners, if that one burns more yellow than the others? That will cause carbony soot.

 

Gas flames burn at a certain speed -- a few feet per second.

Furnace burners are designed to shoot a jet of gas into the burner at a high enough speed so that the flames will burn on top of the burner. If that jet of gas is impaired by low gas pressure or inadequate combustion air, the speed of the gas will be reduced and you can get "flashback" as the flame burns back to the burner orifice, usually making an odd sound.

It sounds like you are describing this flashback condition.

I'd check to see if the burners are clean.

I don't know that you'd be able to recognize other rather subtle problems that are likely causes of this kind of condition.

You may need a good repairman to identify the cause of the problem.

 

Sorry if my question was confusing. Typed it very early in the morning, in a hurry. Yes, only one burner. It will occasionally flashback as you describe on only one burner. I cleaned and found the three burners not put together properly with the little slit that the gas travels between the burners not aligned properly. Thought that I had it fixed, but it still does ocasionally flashback and make an odd noise.

I also posted about having issues with a bad pilot on this same furnace. I have not run the test yet of wathing the burners ignite with the main blower motor not running as I let my furnace fan run year round. I will put the thermostat on auto and watch the burners fire without the blower motor running and report back.

 

It might be worthwhile to remove and clean the burner orifice on the chance that it could be dirty or have some obstruction that impairs the gas flow.

That would be rare, but worth doing to eliminate one possible problem.

 

Yeah, I already cleaned the gas orifice. But now I have done one of the test I have read about. I started the furnace in auto mode, waited for the burners to ignite,(after I lit it with a lighter see my other post about pilot problems) and when the burners ignite, and main fan comes on the burner in question has that flashback where the flame goes all the way to the gas nozzle for a split second, then the burner appears to burn normal. Thank You.

 

yeah, it does it does the flashback thing right when the large fan comes on, not before. It doesn't appear more yellow than the others.

 

If you have a good seal between the blower compartment and the combustion compartment (which you likely do), then unfortunately this would confirm you have a bad(cracked or chunk out of it) heat exchanger,....

....!! which can be potentially dangerous (carbon monoxide poisoning) and needs prompt replacement or replacement of the furnace, before using it any more!! If you do not, you must at least get at least a couple good CO detectors that digitally print out CO levels. Even if you show no reading now, you never know when suddenly the crack gets worse, or even more breakage could occur and a chunk fall out of it (I've seen that, not some theory). And naturally this could happen when you are in bed at about 11pm Friday to Sunday sometime, when it is really cold out.