Intermittent Flame on One Burner at Startup


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Old 03-09-07, 04:55 PM
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Intermittent Flame on One Burner at Startup

Hi,
I have a Janitrol gas furnace (circa 2000) with 4 burners. Call burner #1 the one on the right that has the electronic (glow) ignition. Call burner #4 the one on the far left that has the flame sensor.

When the furnace starts up, burners 1 through 3 light normally (steady flame), but burner 4's flame flickers on and off. The flame is always blue, but sometimes it is there, and sometimes there is no flame.

Sometimes the heat cycle starts normally, but frequently it gives up on the first try (insufficient heat at flame sensor) and has to try again.

It usually lights on the second try, and has only failed to light on the third try once.

Unless I'm imagining things, I think that it actually flickers less on the second ignition attempt.

A friend in the hvac business suggested that I clean the burner nozzle with a wire and clean the flame sensor with fine sandpaper. I did both of those and the problem persisted.

The furnace has behaved like this since day 1. During its first winter, it actually failed to start after 3 tries and gave up (and the house got cold!). A repair man adjusted the flanges on the burner cones. It was starting normally while he was there, but later started showing the startup issue.

Thinking that the cone 'flanges' might be the culprit, and might need more tweaking, I tried swapping the cones for burners #3 and #4 to see if the problem followed the cone. After the cone swap, the intermittent flame at startup stayed with burner #4.

Any suggestions? If a flame cuts in and out, does that point to a gas pressure problem for that burner?

Thanks!
 
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Old 03-09-07, 05:40 PM
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Natural gas, or propane?

What is the vexing question is what is making it improve by try attempt #2 and 3?
 
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Old 03-10-07, 06:24 AM
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It's natural gas.

Good question! (why second attempt is more likely to succeed).

Things (burners, etc.) do heat up a little during the first attempt....

Sorry to confuse things, but my observation about swapping burner cones not having any effect is probably wrong. I watched it start up a few times last night and this morning, and now sometimes burner #3 flickers (where before it never did). Burner #4 still regularly flickers. It even went out totally once on a first attempt.

Can somebody explain the details how the flame is supposed to transfer from one burner to the next at startup? Once a burner lights, should it stay lit on its own w/out 'help from its neighbor'?

Is there a correct way (other than prying with a screwdriver) to adjust the flanges on the burner cones?

Thanks!
 
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Old 03-10-07, 10:44 AM
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Normally there is a crossover pipe that connects all the burner orifices up in succession. If this were plumbing, you'd equate the crossover pipe to a trunk line.
 
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Old 03-10-07, 05:30 PM
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Thanks for posting DaVeBoy.

I knew how the gas gets to each burner (crossover pipe), but I was asking about how the flame is transferred from one burner to the next (at the output end of the burner cones).

I see that the cones have 'flanges' or 'ears' that spread some gas (and flame) toward the neighboring burners' cones. I'd be interested to know about the method (if any) used to adjust these flanges to assure proper flame transmission from one burner to the next. I ask because in 2000 when the repair man came out, I remember him prying on the flange with a screwdriver....
 
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Old 03-10-07, 05:40 PM
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Wink

Is the pilot lighter strip clean. The burner venturi clean ? air shutter set right?? Is the gas psi or W/C set right. gas line to the unit the right size?
The furnace has behaved like this since day 1.
Call the guy that put it in back
 
 

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