2-Stage Trane XL80 Furnace Won't Light; Bad Board, or Ignitor?

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  #1  
Old 12-03-11, 03:07 PM
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2-Stage Trane XL80 Furnace Won't Light; Bad Board, or Ignitor?

I have been out of town for a week, but my wife noticed the furnace was only coming on intermittently. Well, it hasn't lit all day. Filter is new, by the way.

Board error code is "two flashes" meaning External Lock-Out, maximum retries reached. (Sequence of ops for this unit is for the ignitor to warm up for 17 secs while the burner blower spins up, then gas valve opens for 4 secs, and if no ignition, then the main blower starts while the board shuts down for a few minutes for a retry). I hear the board, blower and gas valve go through all of this, just no ignitor glow.

I cleaned the flame sensor with steel wool; nothing. So then I attached a meter to the leads for the ignitor; during the 17 secs "ignitor warm up" cycle, the board provides 94.5 volts of power to the ignitor (which is a White-Rodgers 768-A silicon nitride stick, a la

SILICON NITRIDE IGNITOR | The Ignitor Store )

So...I don't know what voltage the board is supposed to provide.

Bad board, or bad ignitor?

Thanks!
 
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Old 12-03-11, 08:04 PM
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bad ignitor..................................
 
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Old 12-03-11, 09:48 PM
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I was hoping so...an ignitor is a lot cheaper than a board!

The reason I wasn't sure is that I have no idea what voltage the board is supposed to supply, so I couldn't isolate the ignitor.

Just read the spec for the ignitor; it's supposed to be supplied with 80v. Appears we are applying excessive voltage.
 

Last edited by gregger77; 12-03-11 at 11:20 PM.
  #4  
Old 12-03-11, 10:30 PM
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Related question

Hey again

I also read that voltage from the board will go too high if the ground connections are bad. Well, I looked at the junction box inside the furnace, and the green wire that goes from the ground screw (inside top of the box) is about 6" long, stripped end, and connected to NOTHING. I think maybe it was twisted around a screw to the inside of the cabinet; or maybe just jammed into the cabinet door hinge...because there is nothing else nearby it would have been connected to.

So...separate question, how is a ground usually achieved with the ground wire from the furnace's junction box?

Thanks!
 

Last edited by gregger77; 12-03-11 at 11:21 PM.
  #5  
Old 12-04-11, 04:42 AM
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do you have a gound wire coming in wit the power wires? Is there metal conduit attached to the furnace containing the power wires? Typically the furnace wont run unless it "sees" a ground. What kind of meter are you using to measure the voltage? A poor meter will give you false readings. However, those nitride HSI hardly fail very often so there is most likely a cause for it to have failed. Trane has also updated that ignitor: Part number IGN00145
 
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Old 12-04-11, 09:17 PM
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Yes, there's solid metal conduit coming from the service to a gang box with a toggle power switch mounted to the side of the furnace, and then flex conduit takes the power into the furnace's own gang box inside. So I guess that's providing the ground.

I'm using a light-duty digital multimeter from Home Depot. It reads my AC supply very consistently at 121 v for whatever that's worth!

I guess I can replace the ignitor and then monitor the board voltage going to it occasionally and if it remains high (in the 90s), consider changing the board.

Re: ignitor number, IGN00145 is sort of a "genetic" number for Trane, Am Standard, and others, right? It seems to be a cylindrical-based unit, vs the rectangular base unit I have now (which is Trane P/N B340971). Are you saying I will now be going to a different shape and mounting bracket?

Thanks,

--G.
 
  #7  
Old 12-04-11, 09:28 PM
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[/INDENT]PS This link shows the ignitor I have, with the Trane cross ref number that is on mine (B340971). So...this is being sold here and on a large number of other websites...but I should not be using it?

White-Rodgers 768A-845 Replaces White-Rodgers 768A-5, Trane B340970P01

Thanks
 
  #8  
Old 12-05-11, 03:00 AM
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TRANE upgraded your ignitor to the round one and with IGN00145 it comes with the new mounting bracket. Many places sell the old ignitor (your current style) but they are new OLD stock. IGN00145 is a TRANE part number and is not a universal number. P/N B340971 is manufactures number and is not a TRANE number. All TRANE ignitors start with IGN

I would consider removing your control board to examine the backside for burn/hot marks.........
 
  #9  
Old 12-05-11, 07:41 AM
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Will do. In the meantime, I have gone ahead and ordered the IGN00145 to at least get the heat going again. Got our first snow flurries this morning and it's not getting any warmer inside the house...

Not sure how hard it is to remove control board; guess I should take a cell phone shot to be sure I don't mess up connex.

Where would I be looking for hot marks in particular? I'll take a shot of that too. Will report back.

Many thanks for your kind help.

-- G.
 
  #10  
Old 01-01-12, 01:03 PM
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Sorry, forgot to wrap up this thread. The ignitor arrived, and the furnace immediately fired up. I guess 8 or 10 years out of an ignitor is not bad...that's how old the furnace is. The board must be doing a pretty good job of managing the voltage to the ignitor; I read the tech manual, and found it has logic that tapers the voltage down as low as possible over time to preserve the life of the ignitor.

Thanks all for the great advice.
 
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