Lennox G50UH(X) Low Flame Failure Mode


  #1  
Old 01-26-08, 02:46 PM
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Lennox G50UH(X) Low Flame Failure Mode

Hello,

I tried to put as much info in this post as I could, so please be patient with the length

I have the furnace quoted in the thread title. This has only happened 4-5 times, but when it does the furnace does not work correctly and the "Low Flame" warning lights come on. What happens is the ceramic ignitor glows orange, gas is emitted, the four burners are lit, stay on for 4 seconds, then go out. The "Low Flame" warning lights are then displayed. The "Watchguard" mode in the furnace then has a cycle it goes through where it will then try to light the burners 3-4 additional times, and if the "Low Flame" failure mode occurs each additional time, the furnace will go into safety mode and blow cold air for 60 minutes before trying to meet the heating demand again.

In the troubleshooting section of the user's manual it says to check the ignitor to see if it glows orange, if it does, it's not the ignitor. Mine glows orange, so that's not the problem.

Then, they say to check the flame sensor, which is a metallic wand that extends downward in front of one of the four burners, and is heated(?) by one of the flames. One suggestion the manual makes is to polish the sensor wand with steel wool. Here is what it says in the manual and what the troubleshooting possibilities could be:

6.2 - Burners Light with Heating Demand but fail to stay lit. Sequence:
− Combustion air inducer energizes
with a heating demand.
− Burners light but fail to stay lit.
− After 5 tries the control diagnostics
flash the watchguard burners failed to ignite.

Possible Problems, Solutions:

6.2.1
Sensor or sense wire is improperly
installed.

ACTION 1 − Check that sensor is properly located
and that the sense wire is properly attached
to both the sensor and the control.

6.2.2
Sensor or sense wire is broken.

ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense
wire. If wire or sensor are damaged replace the
ignite code component.

6.2.3
Sensor or sensor wire is grounded to
the unit.

ACTION 1 − Check for resistance between the
sensor rod and the unit ground.
ACTION 2 − Check for resistance between the
sensor wire and the unit ground.
ACTION 3 − Correct any shorts found in circuit.

6.2.4
Control does not sense flame.

ACTION 1 − Check the microamp signal from
the burner flame. If the microamp signal is below
0.70 microamps, check the sense rod for
proper location or contamination.
ACTION 2 − Replace, clean, or relocate flame
sense rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN ROD
WITH SAND PAPER. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM. NOTE: Do not attempt to bend
sense rod.
ACTION 3 − Check that there is proper ground
to burner box. Repair as necessary.

I guess my question is whether I should spend the $ to call a furnace guy or just try the steel wool thing, and if I do, what type of steel wool should I use and how hard should I rub? I bought the very fine type of wool that is used for polishing metals. It can't be a broken wire or the furnace would never work, and this has only happened a few times. I know what a multimeter is but I wouldn't know enouch about where to how to check the resistance in the wires, etc. Unless someone could explain it to me briefly.

I wouldn't even worry about this normally but my wife and I are going out of town for 6 days and I don't want the furnace to fail and the pipes to freeze. Peace of mind kind of thing.

Thanks in advance to anyone who can provide advice.
 
  #2  
Old 01-26-08, 03:38 PM
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Steel wool polish the rod on the flame sensor and your troubles will be over. Finer steel wool is perfectly effective. All you are gettting off is this tarnish.
 
  #3  
Old 01-26-08, 04:30 PM
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Thanks ecman for your advice.
 
  #4  
Old 01-26-08, 04:43 PM
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I'll add that the 4 second business is the real clincher. That is about the exact time allowance for the sensor not detecting flame and then it shuts off the glow and the gas.
 
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Old 01-26-08, 05:00 PM
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Thanks, that really helps. Just starting to learn about all of this stuff being a new homeowner and all. Baby steps...
 
  #6  
Old 01-26-08, 05:29 PM
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One other question, I live in a townhome where the furnace is in the front hallway closet off of the kitchen. The closet doors have 2 inches underneath for airflow, and my furnace isn't a spark ignition. However, there is a duct in the closet that brings in cold air directly from the outside. Is this duct necessary for proper furnace performance, or can I close off the duct? It really brings in a pretty sizeable draft and I wonder if it makes the furnace kick on more than it should, raising my heating bill.

Perhaps I could at least put some duct tape over the duct opening to make it smaller but not completely close it off?

Thanks.
 
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Old 01-27-08, 12:58 PM
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Try dangling toilet paper vertically down the outside of that door, with the toilet paper just barely off the ground, have the furnace run and see what that toilet paper tries to do. Does it want to suck under the door? Or does it push outward? And what does the toilet paper do if you have the furnace off and turn on your dryer and run bath fan?
 
  #8  
Old 04-18-08, 05:02 PM
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Flame sense issue

Hi, I have that issue with a pizza oven that works with a very similar ignition system, and my recomendation is to replace the flame sense rod, because I tried several times to clean it the way the manufacturer suggests and didn´t work until I replaced it and problem solved, actually that same issue happens every 3 or 4 months, so I decided to replace it every 3 months before it starts to give me the hard time and I always keep a couple of flame senses in stock, anyways they´re not so expensive.

Originally Posted by Swerve01
Hello,

I tried to put as much info in this post as I could, so please be patient with the length

I have the furnace quoted in the thread title. This has only happened 4-5 times, but when it does the furnace does not work correctly and the "Low Flame" warning lights come on. What happens is the ceramic ignitor glows orange, gas is emitted, the four burners are lit, stay on for 4 seconds, then go out. The "Low Flame" warning lights are then displayed. The "Watchguard" mode in the furnace then has a cycle it goes through where it will then try to light the burners 3-4 additional times, and if the "Low Flame" failure mode occurs each additional time, the furnace will go into safety mode and blow cold air for 60 minutes before trying to meet the heating demand again.

In the troubleshooting section of the user's manual it says to check the ignitor to see if it glows orange, if it does, it's not the ignitor. Mine glows orange, so that's not the problem.

Then, they say to check the flame sensor, which is a metallic wand that extends downward in front of one of the four burners, and is heated(?) by one of the flames. One suggestion the manual makes is to polish the sensor wand with steel wool. Here is what it says in the manual and what the troubleshooting possibilities could be:

6.2 - Burners Light with Heating Demand but fail to stay lit. Sequence:
− Combustion air inducer energizes
with a heating demand.
− Burners light but fail to stay lit.
− After 5 tries the control diagnostics
flash the watchguard burners failed to ignite.

Possible Problems, Solutions:

6.2.1
Sensor or sense wire is improperly
installed.

ACTION 1 − Check that sensor is properly located
and that the sense wire is properly attached
to both the sensor and the control.

6.2.2
Sensor or sense wire is broken.

ACTION 1 − Check for a broken sensor.
ACTION 2 − Test continuity across the sense
wire. If wire or sensor are damaged replace the
ignite code component.

6.2.3
Sensor or sensor wire is grounded to
the unit.

ACTION 1 − Check for resistance between the
sensor rod and the unit ground.
ACTION 2 − Check for resistance between the
sensor wire and the unit ground.
ACTION 3 − Correct any shorts found in circuit.

6.2.4
Control does not sense flame.

ACTION 1 − Check the microamp signal from
the burner flame. If the microamp signal is below
0.70 microamps, check the sense rod for
proper location or contamination.
ACTION 2 − Replace, clean, or relocate flame
sense rod. If rod is to be cleaned, use steel
wool or replace sensor. DO NOT CLEAN ROD
WITH SAND PAPER. SAND PAPER WILL
CONTRIBUTE TO THE CONTAMINATION
PROBLEM. NOTE: Do not attempt to bend
sense rod.
ACTION 3 − Check that there is proper ground
to burner box. Repair as necessary.

I guess my question is whether I should spend the $ to call a furnace guy or just try the steel wool thing, and if I do, what type of steel wool should I use and how hard should I rub? I bought the very fine type of wool that is used for polishing metals. It can't be a broken wire or the furnace would never work, and this has only happened a few times. I know what a multimeter is but I wouldn't know enouch about where to how to check the resistance in the wires, etc. Unless someone could explain it to me briefly.

I wouldn't even worry about this normally but my wife and I are going out of town for 6 days and I don't want the furnace to fail and the pipes to freeze. Peace of mind kind of thing.

Thanks in advance to anyone who can provide advice.
 
  #9  
Old 12-04-08, 08:47 PM
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Thumbs up Steel wool

I tried the same steel wool cleaning on flame sensor on our Lennox 3 ton heater, where it would light and then go out and we are happy to say it worked and we are warm. Thanks to you experts for the indirect help. Mack
 
  #10  
Old 04-19-09, 12:48 AM
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Heating issues

This worked for my Lennox G50UH as well. Thank you.

-brad
 
 

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