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Discussion Starter · #1 ·
Hello. My furnace displays a 12 fault code. I've replaced the pressure switches, control board, flame sensor, and limit switch, I have a new capacitor and a new ignitor to swap out the respective components. The sequence: a call for heat will initiate the blower, in about 90 seconds the ignitor will glow and the firing sequence will begin. Of three burners, the first and second burner will ignite but the third fails and the sequence will start over for a total of three times and then the furnace will shut down. Subsequent calls for heat fail until I cut and restore power several times. Second issue that I'm having is that the furnace will not heat to the thermostat temperature setting. Any ideas or assistance is appreciated.
 

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Code 12 just just means that the furnace is receiving a call for heat. When the power is turned back on to it.

May have a dirty cross over on the burners, that it is not igniting all the burners.
 
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Discussion Starter · #3 ·
Code 12 just just means that the furnace is receiving a call for heat. When the power is turned back on to it.

May have a dirty cross over on the burners, that it is not igniting all the burners.
Thank you! Just for my clarification, is the "crossover" aka the manifold?
 

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Agreed but the furnace is probably about 25 years old. The inducer motor was making noise and a tech that was out here last year said the control board should be replaced and that the capacitor was weakening. I considered it an investment in prevention and overall improvement of the existing appliance.
I'm also speaking to a local HVAC service provider whom I'm ready to call in for service. Thank you for your kind assistance.
 

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Take all the burners out and when you look at the front of them it looks like a wing and there are slots in them. The gas flows from one burner to the other to light them. Clean them out with a small file or nail if they are rusty.

I usually pull the burners and if you have compressed air blow them out. Then rinse them in hot water in a sink and dry them. That removes any internal dust.

Look inside the burners for debris and in the front of them. If there is a steel ring with holes in it ( diffuser ) and those holes are plugged clean them also.

Make 100% sure you label the burners with a black sharpie first and don't mix them up when putting back in. Some of them are very finicky as to which burner sits where.
 

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Discussion Starter · #7 ·
Take all the burners out and when you look at the front of them it looks like a wing and there are slots in them. The gas flows from one burner to the other to light them. Clean them out with a small file or nail if they are rusty.

I usually pull the burners and if you have compressed air blow them out. Then rinse them in hot water in a sink and dry them. That removes any internal dust.

Look inside the burners for debris and in the front of them. If there is a steel ring with holes in it ( diffuser ) and those holes are plugged clean them also.

Make 100% sure you label the burners with a black sharpie first and don't mix them up when putting back in. Some of them are very finicky as to which burner sits where.
Thank you! I tried sticking a paper towel in there but it's too tight a fit. I was thinking of disassembling and taking them out to clean them. I'll check the diffusers too. I also thought about the air compressor too. Thank you so much!
 

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Thank you! I tried sticking a paper towel in there but it's too tight a fit. I was thinking of disassembling and taking them out to clean them. I'll check the diffusers too. I also thought about the air compressor too. Thank you so much!
Yur Welcome :)
 

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Everyone is correct. The flame sensor ( which sits near the last burner) is not proving that the last burner is coming on which will cause the blower to come on for x seconds as to purge the burner section and then tries again over and over. The burners are probably dirty and the track that conducts the flame from one burner to the other is blocked. if you dont have air compressor, a Wire brush works for me. you will most likely need to remove each of the burners and that may require removing the manifold
 

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Discussion Starter · #10 ·
Everyone is correct. The flame sensor ( which sits near the last burner) is not proving that the last burner is coming on which will cause the blower to come on for x seconds as to purge the burner section and then tries again over and over. The burners are probably dirty and the track that conducts the flame from one burner to the other is blocked. if you dont have air compressor, a Wire brush works for me. you will most likely need to remove each of the burners and that may require removing the manifold
Thank you for your insight. I blew out the burners with a the compressor nozzle. It worked like a charm and I'm glad! I didn't want to take those burners apart. It looked like a major endeavor. Thanks to all, I appreciate all the good advice! Happy new year!
 

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Thank you for your insight. I blew out the burners with a the compressor nozzle. It worked like a charm and I'm glad! I didn't want to take those burners apart. It looked like a major endeavor. Thanks to all, I appreciate all the good advice! Happy new year!
Good Job. FYI: Next time you perform a preventative maintenance routine, watch the burner ignition to see if any of the other burners hesitate to ignite which would indicate the beginning of a build up of debris or some oxidation wear between the burners. Also the flames should look similar across the burners and show very little change once the main Blower comes on. If the flames dramatically (there will be some, slightly) change color and flap just as the blower starts up, that could indicate a crack(s) in the heat exchange. Since you changed a few of the key parts, do check the capacitor with a Capcitance Meter (inducer motor and main blower if applicable) even though the motor are working. Drifting capacitor values will make the motors run sub optimal. Have a great new year.
 

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Discussion Starter · #12 ·
Good Job. FYI: Next time you perform a preventative maintenance routine, watch the burner ignition to see if any of the other burners hesitate to ignite which would indicate the beginning of a build up of debris or some oxidation wear between the burners. Also the flames should look similar across the burners and show very little change once the main Blower comes on. If the flames dramatically (there will be some, slightly) change color and flap just as the blower starts up, that could indicate a crack(s) in the heat exchange. Since you changed a few of the key parts, do check the capacitor with a Capcitance Meter (inducer motor and main blower if applicable) even though the motor are working. Drifting capacitor values will make the motors run sub optimal. Have a great new year.
THANKS!
 
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