Burner will not stay lit


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Old 12-21-10, 09:57 PM
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Burner will not stay lit

Hi,

Need help with a little direction on fixing a problem. I have a Carrier 58PAV070-12 heater and the burner will not stay lit. Well, to be exact, it is actually lit now and working. However for the last day and a half, the it would only stay lit for 3 seconds and go out; lite up again and go out; etc. The test codes came back as 11, which obviously means nothing.

I assume that there may be some build up somewhere but some advice on what/how to clean (if that is recommended) would be much appreciated. I travel for work and I'd rather not have this happen to my wife when I am 3000 miles away.

Thanks,
John
 
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Old 12-21-10, 10:04 PM
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Old 12-21-10, 10:09 PM
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Originally Posted by lawrosa
Thanks but the HSI is fine; gas comes, flame is lit for 3 seconds or so, then goes out. I assume if it was HSI then it would not lite at all...
 
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Old 12-21-10, 10:12 PM
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Since the burners are lighting the hot surface ignitor isn't the problem.


COULD be a flame sensor that needs cleaning. At least that would be an easy guess to try.


The flame sensor is on the opposite side of the furnace from the igniter. It's a thin rod sticking up into the main burner flames with a wire from the bottom going back to the ignition module.

Remove it and use a wire brush to clean the invisible oxides that can coat the sensor, preventing it from detecting that the burner flames are lit.

Usually I'd expect an error code pointing to that, but it's an easy thing to try and ordinary maintenance that should be done annually anyway. So start there.
 
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Old 12-21-10, 10:28 PM
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Originally Posted by SeattlePioneer
Since the burners are lighting the hot surface ignitor isn't the problem.


COULD be a flame sensor that needs cleaning. At least that would be an easy guess to try.


The flame sensor is on the opposite side of the furnace from the igniter. It's a thin rod sticking up into the main burner flames with a wire from the bottom going back to the ignition module.

Remove it and use a wire brush to clean the invisible oxides that can coat the sensor, preventing it from detecting that the burner flames are lit.

Usually I'd expect an error code pointing to that, but it's an easy thing to try and ordinary maintenance that should be done annually anyway. So start there.

Thanks, I will give that a try - I did see the flame sensor...will update tomorrow.
 
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Old 12-22-10, 09:06 PM
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I cleaned the flame sensor fairly well with steel wool; still seems to be a problem. Not sure if it matters but the flame is 95% blue...very little orange.

Thanks!
 
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Old 12-22-10, 10:08 PM
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The flame rectification system checks to verify that the burners hyave lit once the main burner gas is turned on. You don't want gas coming out if it doesn't light. If that test isn't met within three seconds or so the gas is shut off.

That's what appears to be happening with your furnace, but the burners ARE lighting so the gas should stay on.

That implies that the flame sensing system isn't working. Usually I'd expect the specific diagnostic code for that condition to be signaled, but that apparently isn't happening.

You need to test the rest of the flame rectification system.

An AC voltage is applied to the flame sensor via the wire. When the burners light and the flame touches the flame sensor, a small DV current flows from the flame sensor to ground. That DC current is what the ignition control should detect and then leave the gas on.

So check to verify that the flame sensor is indeed engulfed when the burners shut off improperly.

Then measure and report the AC voltage on the flame sensor when the gas valve should be on.
 
 

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