Bryant 80% furnace, only one burner firing intermittently.

[ComfortablyNumb]

Working on a Bryant 80%, model #: 310AAV03607AAJA manufactured in '02.

Had a client call in, saying every other day or so the unit locks out and must reset power to control. Unit is running when I arrived, and the only issue I saw of ANY question was slightly low manifold pressure of 3.35" and a semi-dirty flame sensor. After cycling it numerous times hoping to see some action, it finally showed the phantom and only 1/3 burners ignited, being the burner nearest to the HSI. I still had my manometer in the manifold pressure tap, and when this occurred there was no change in pressure. 4 trials and then lockout. It did this once more on the next cycle after reset, 4 trials then lockout. I dismantled the manifold, removed and check orifices as well as the manifold and it was all clean. Removed the burners (uni-burner style assembly) and checked cleanliness. Clean as a whistle. Reassembled and tested again, fired normally the first time, then same problem repeated the next cycle after reset. Cycled another time without adjustment and fired normally.

I then adjusted the manifold pressure to 3.5", and the last few times I cycled the unit it fired normally. The call was already a late one, and by now it was nearing 8pm and I was an hour from home, and the unit wasn't locking out at this point. The client was okay with resetting if need be to see if the problem returned this weekend. So I parted ways.

I really didn't think that a small difference in manifold pressure could create this issue, and with an intermittent problem as such, just because the client has not called back in I'm not 100% confident that was the issue.

Being that I was getting basically-normal and consistent manifold pressure through the pressure tap, while on site I'd ruled out a glob of Rectorseal from the field connection side of the gas valve being the culprit. Please correct me if I'm wrong.... as when I was driving away I was somewhat kicking myself in the ass for assuming and not ruling out that possibility.

I've seen this happen 2 other times in my career, once being a failing modulating gas valve and the other being a dirty burner assembly. And we are mostly a heat pump market in my area for residential, so maybe this happens more often than I am aware of.

Obviously 2-stage and modulating valves fire at a reduced manifold pressure far below 3.35"... so I'm not convinced this was the problem, aside from the assumption those units are designed to fire at a reduced pressure, and this 80% furnace is not. Not to mention I've seen 80% units fire just fine at a slightly reduced pressure before adjustments on PMs.

I'm at a loss at the moment, with somewhat hurt pride as we all sometimes experience, just waiting for the fella to call back in.

Any thoughts/theories/comments welcome! Thanks.

[rich pickering]

run a small flat blade screwdriver between the fins of the pilot run. IIRC you should be able to run a dime between them.

[ComfortablyNumb]

run a small flat blade screwdriver between the fins of the pilot run. IIRC you should be able to run a dime between them.

Done. Could easily fit a dime between them....

[stay gold jonny]

Where is the furnace located in the house, I have found furnaces located in laundry rooms that have the same problem. What happens is all the fragrances from detergents and fabric softeners can cause these problems. If you can smell it, it can be drawn into the furnace. I pull the burners and wire brush em real good and if there's a sink near by I will wash them off with water, then dry them of coarse. That solves the problem for me. Every time I come across this the burners look clean and can have me second guessing. Hope this helps.

[ComfortablyNumb]

Where is the furnace located in the house, I have found furnaces located in laundry rooms that have the same problem. What happens is all the fragrances from detergents and fabric softeners can cause these problems. If you can smell it, it can be drawn into the furnace. I pull the burners and wire brush em real good and if there's a sink near by I will wash them off with water, then dry them of coarse. That solves the problem for me. Every time I come across this the burners look clean and can have me second guessing. Hope this helps.

The unit is horizontal in an attic. But damn thats interesting... like it gives the burners a strange coating or something? I did give them a good wire brushing just for good measure even though everything looked clean... but I didn't rinse them. I'll do that as well if/when I end up back out there. Good info on the laundry room location nonetheless, I'll be keeping that in mind.

[firecontrol]

When all did light, did all three flames look normal and transition into the HE the same?

[syndicated]

Done. Could easily fit a dime between them....

If you can easily fit a dime in there then they're too big. The space should *just* be the height of a dime.
Definatly clean the burners really really well though, then make sure they'd assembled properly, with the overlapping tabs in the right place.
Maybe use a pipe cleaner to gently clean the orifices as well.
I've seen something as small as a piece of dryer lint block the flame from moving across the rail.

[dgussler]

Sounds like something in manifold assembly intermittently clogging up one of the orifices. If one burner does not light due to clogged orifice the other burners in line with it will not light either due to the flame not traveling across the rail.

[ComfortablyNumb]

When all did light, did all three flames look normal and transition into the HE the same?

When I first got there, before I knew what was causing the lockout, and cycled the unit numerous times with normal operation the burners were igniting smoothly and normally. But after witnessing the problem of only one burner lighting, the next couple full ignitions were indeed a bit odd. Not as smooth, sort of delayed, more of a "poof" than a smooth transition if that makes sense.

If you can easily fit a dime in there then they're too big. The space should *just* be the height of a dime.
Definatly clean the burners really really well though, then make sure they'd assembled properly, with the overlapping tabs in the right place.
Maybe use a pipe cleaner to gently clean the orifices as well.
I've seen something as small as a piece of dryer lint block the flame from moving across the rail.

Well that was more of a figure of speech and going by memory. Let's just say they appeared clean and normal.

And there's no way for the burners to not be assembled properly, as the "burners" are one single assembly, whatever the name for that style may be.

When/if I end up back out there after the holidays I will give them another cleaning... and clean the orifices. They were very clean already but I will for good measure.

Sounds like something in manifold assembly intermittently clogging up one of the orifices. If one burner does not light due to clogged orifice the other burners in line with it will not light either due to the flame not traveling across the rail.

It seemed like that would be the case... but I did take apart the manifold and looked for such a problem. If there's something in there it would be very elusive.

[ch4man]

does the inducer motor have a cooling fan blade??

ive seen these disrupt ignition and /or crossover.

carrier had a shield kit for this.....

call your distributor to see if your model applies.

not saying, just saying.....................

[dgussler]

If you could get in situation where only one burner lights next time I would take one end of paper clip or something small and stick up through the next orifice not lighting, then i would initiate another call for heat and see if it lights

[ch4man]

If you could get in situation where only one burner lights next time I would take one end of paper clip or something small and stick up through the next orifice not lighting, then i would initiate another call for heat and see if it lights

and if it does light?

what will that mean?.

[dgussler]

and if it does light?

what will that mean?.

I apologize I did not thoroughly explain myself. The whole purpose of sticking a paper clip through the orifice is to clear out any obstructions. After removing the paper clip and the burner lights after the next ignition sequence, then we know good and well that there was something obstructing that particular orifice. Of course this will only be a temporary fix. In this case The whole manifold assembly should be pulled and cleaned blew out with nitrogen etc.. Although he stated he had already cleaned out the burner manifold assembly there still may be something small in that manifold. Does not take much to stop up a orifice.