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Old 11-15-2012, 09:58 PM   #1
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furnace wont stay on


Hey I have a carrier package unit (model - 48gs-030060301), The furnace will spark and pilot will lite. A few seconds later the burners will fire. Blower kicks on and Furnace runs about 1 minute then shuts off on a roll out fault. I dont think it is a bad switch because I can see the flame (kick back) just before she shuts off.

What would make a (sloppy) flame? It is very sloppy even while it is running. I only seen a straight flame that goes into the exchanger before now. Only about 60% of this flame is going into the exchanger, the other 40% is all missing the ports to the exchanger high. It is almost like it is to much gas pressure, but I could not find the port to measure the pressure.

I did find a burn spot on the control board but it doesn't look that bad and looks like it has been there for some time.

What can I check first and how can I tell for sure if I have a cracked heat exchanger?

Thanks for the help

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Old 11-15-2012, 10:01 PM   #2
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furnace wont stay on


Hey I have a carrier package unit (model - 48gs-030060301), The furnace will spark and pilot will lite. A few seconds later the burners will fire. Blower kicks on and Furnace runs about 1 minute then shuts off on a roll out fault. I dont think it is a bad switch because I can see the flame (kick back) just before she shuts off.

What would make a (sloppy) flame? It is very sloppy even while it is running. I only seen a straight flame that goes into the exchanger before now. Only about 60% of this flame is going into the exchanger, the other 40% is missing the ports to the exchanger high. It is almost like it is to much gas pressure, but I could not find the port to measure the pressure.

I did find a burn spot on the control board but it doesn't look that bad and looks like it has been there for some time.

What can I check first and how can I tell for sure if I have a cracked heat exchanger?

Thanks for the help

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Old 11-15-2012, 10:11 PM   #3
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furnace wont stay on


If the flame is "kicking back" and tripping the roll out switch then an exchanger fault is quite possible. If this "kicking back" back occurs as soon as the fan blower turns on then it's likely.
You can pull the burners and scope with a camera, check the hot air plenum before the blower comes on for CO but most likely it will be more cost effective to get a tech in with the right equipment and the knowledge of how to use it.
Overgassing is possible and that can be explored with either a manometer or the clocking of the meter.
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Old 11-15-2012, 11:03 PM   #4
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Watch the flame before the blower starts. If the blower starts and the flame starts to dance it is one indicator of a cracked exchanger....but start there.
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Old 11-15-2012, 11:25 PM   #5
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No it is all over the place before, the fan even comes on. what would cause that? Im not sure how I missed the plug to test pressure, but I think I may need to check pressure.

Last edited by subcool; 11-15-2012 at 11:45 PM.
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Old 11-16-2012, 08:34 AM   #6
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Im not sure why this thread is in here twice but . . . When the flame first comes on it is all over the place, before the fan starts. That would make me think it is not a heat exchanger. What could make it all over the place from the time the flame comes on.

Thanks for the help.
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Old 11-16-2012, 10:15 AM   #7
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Heat exchanger is probably partially plugged with rust or soot and that is from bad combustion which may be related to the cracked heat exchanger. Should get it properly checked by a Pro.
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Old 11-16-2012, 03:42 PM   #8
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okay new update the flame is all over the place before the fan comes on, but yes when the fan comes on it blows it out the flame.
I did take an inspection camera and shove it up the exchanger and did not see a crack, I opened up the shell and looked all around each side of the heat exchanger except for the side facing the fan and still nothing.

does that mean it is the exchanger? i just don'twant to buy another one of i don't need it.





thanks again for all the great help
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Old 11-16-2012, 03:44 PM   #9
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Buy another one, safest bet.
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Old 11-16-2012, 05:52 PM   #10
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Doed this unt have an induce draft blower? Sounds like a clogged exaust, however, if it has an induced draft blower it should not start if the pressure switch is working properly.
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Old 11-16-2012, 07:46 PM   #11
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Those heat exchangers are good at rusting up. Open the access cover so you can see the tubes and look for rust on the seams. Push on the rust spot with your fingernail and it will go right through most of the time.

When the flames can't make it through an exchanger the carbon monoxide goes from a few parts per million to several thousand ppm so don't be breathing any fumes. Ten thousand ppm will kill you in under 2 minutes.
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Old 11-16-2012, 10:53 PM   #12
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Quote:
Originally Posted by danpik View Post
Doed this unt have an induce draft blower? Sounds like a clogged exaust, however, if it has an induced draft blower it should not start if the pressure switch is working properly.
Yes it does have a draft blowe, and I didn't think to check it because I could hear it, and if it wasn't working it should start, right? That is what I thought as well. It seems there is enough pressure for the pressure switch but not enough for the flame. When I feel around the side of the unit there is no air coming out of the draft vent. I am going to head back out tomorrow and check the blades I bet they are rusted or gone.

But still that would not explain why the flame is all over the place, but once again once the blower starts the flame goes out. Has to be a cracked exchanger as well, right?
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Old 11-16-2012, 10:57 PM   #13
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not cracked for sure....you must inspect it..... does not sound good though....
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Old 11-16-2012, 11:43 PM   #14
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An ID that continues to cause a flame rollout would also require a pressure switch to work with a coresponding lower pressure drop than what it's designed for. A PS always become less sensitive or fails. I've never seen one become more sensitive than what it's designed for.
The burner problem can occur from being overgassed or the burner diffusers being debris filled but the timing of the flames being affected by the main blower coming on just says you have a real big crack in the exchanger.
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Old 11-16-2012, 11:47 PM   #15
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I agree it suggests you have a major crack...prove it...... open it up and look in....

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