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Ignitor failure mystery

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5.3K views 17 replies 8 participants last post by  mttrhll  
M
#1 ·
I have a recurring problem that neither techs nor myself can figure out. Ignitors burn out 1 or more times a year on my furnace.

I had a tech out and he saw 2 potential issues:

  1. The control board looked a little "rough", but no diagnostics have shown anything directly wrong. He said he saw voltage from 67 to 125 volts out of the control board. Based on reading this is within the specification.
  2. The gas valve's pressure was a little below spec. It was measuring 2.97, he said it should be 3.5.


Do either of these sound like they could be the root cause? I mean i'd think the control board would be doing lots of weird stuff or at least the voltage to the ignitor would be way out of spec if it was faulty.

I'm trying to decide between replacing the whole furnace, replacing the control board and the valve or just the control board.

There are more details below if it helps. Hopefully someone has encountered a similar problem. Thanks!!!

Here are some other details:
  • The original ignitor lasted 10+ years.
  • The furnace is a Lennox 80UHG4/5 - 120 - 3
  • The ignitor model I have been using is white-rogers: 768A-844 on the box it says it replaces 768A-4. I think the one that was in it was part # 41K56 ... pretty sure the one i've been using is the replacement.
  • This unit was installed in 2001
  • The blower motor was replaced several years ago... i think at least 2 years before this ignitor problem.
  • The flame sensor has been cleaned many times and measures correctly
 
Z
#4 ·
I laugh... when I worked at a certain supply house, I was told to sell to homeowners whatever they asked for. But never suggest the correct part. That way it would keep them coming back. Needless to say, I have scruples and don't work there anymore.
 
M
#5 ·
Every lookup says it is the correct model... even the box has the matching model. Is there a place you suggest to check this? I've checked tons of sights, the box and forums. All seem to point to this model. The control board is model # 50A65-120 ... its replacement seems to also use the 768A-844 ignitor :(
 
#6 ·
Please explain igniter "burns out"? Is it burning in two and the end falls out of the flame or is it getting dirty and has to be cleaned so much that it wears out, or does the igniter ceramic go bad, or . . .

There is a lot of stuff that can happen with an igniter. A little more specifics would be nice. What symptoms are you experiencing? What readings have been taken, V, uA, grounds . . .?
 
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M
#7 ·
It stops igniting - won't light up. The few I have checked then read incorrect ohms. I have checked like 4 or 5 that exhibit this failure.

They do not disintegrate or burn up... they look the same as new, but won't light. I pop a new one in and it begins working again.

Edit: Tech measured the voltage during ignition after we installed the latest one. That is what i put in my original post. He measured "67 to 125 volts".

I measure the ohms of one that would not ignite... it was measuring 66... a replacement i have measures about 15 ohms.
 
#8 ·
mttrhll said:
It stops igniting - won't light up. The few I have checked then read incorrect ohms. I have checked like 4 or 5 that exhibit this failure.

They do not disintegrate or burn up... they look the same as new, but won't light. I pop a new one in and it begins working again.
Click to expand...
Have you tried shutting power off and trying it again to see if it will work? You said the voltage would run from 67-125, how long does it stay below 90V?
 
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#11 ·
When I said "clean" I was having a brain phart and thinking sensor, not igniter.
 
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#10 ·
Have you tried OEM parts?

Those part numbers are aftermarket parts, while they may be made for Lennox by that MFR, there may be something different.

Reading variying voltage is concerning, unless this is proper for that unit. Trane had a unit that tried to save energy/parts by varying voltage to the ignitor, they have since altered replacement parts to get rid of this. Too many issues with ignitor failures.
 
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M
#14 ·
So I just looked at the failed ignitor more closely... the ignitor surface seems to be worn off, basically where the flame contacts it. I'm not sure they all looked like this after failing. I can't post an image yet so I'll attach include it when I can. Not sure why that would be happening.
 
M
#17 ·
It is the original board i'm pretty sure... I can snap a picture... but even the original part that lasted several years was a 41K5601 i believe. It was an "80V" but these ignitors and boards all did the variable voltage thing... It rtries to figure out the lowest ignition voltage.

I've checked this again and again... and i've had 2 HVAC techs from reputable companies come out and try to diagnose this... but if someone can point me to some resource i'd be happy to do the research.

Losing heat in Ohio randomly is stressful... Thanks for everyone's ideas so far.
 
M
#18 · (Edited)
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