Trane XL80 Gas Furnace - Random No Gas after Igniter Glows

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Old 11-14-11, 09:51 AM
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Trane XL80 Gas Furnace - Random No Gas after Igniter Glows

So been monitoring my furnace on and off for few weeks. Initial issue has been no heat, and I walk up to an 7 blink error. According to schematic on panel, thats something like an "external lockout" Excuse my exact verbiage, going from memory and Im not at home right now. Typically can flip power switch at unit, which resets and typically works shortly after that. So been headache to catch what the issue is.

But, I finally saw it! Been keeping the top cover off, not the fan/motherboard cover on the bottom, but the top burner cover off. I saw the orange glow on the right side, heard and saw gas come on briefly, then before all burners ignited the gas shut off. The last burner on far left has the sensor that validates the flame actually came on, so since only about half the burners ignited... the lockout error makes sense. I un & re-plugged the gas switch connector a few times, think I helped it. But since it is intermittent any way and weather changes... probably just my imagination.
Since then, issue still exists but I never have caught the partial gas flow again. I always see the glow and It either just gets no gas at all, or plenty. Rarely does it fail twice in a row. And usually it's fine, when I walk up to it and reset it, hence the challenge to figure out whats going on.
I think the system is designed to auto reset after an hour, purely my assumption... but I think that is why it tends to work on not so cold days. Cause eventually will work after an hourly attempt is successful. Then it catches up to temp setting, and all is well. But colder days are less forgiving to consecutive failed auto retries, then I walk downstairs reset and it works????

Please provide some guidance, what and how should I be checking next?

My guess is faulty gas switch, but been just starting to read 'bout pressure switches, not sure yet if I should care?

Thanks in advance!
 
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Old 11-14-11, 10:58 AM
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Yes, it's quite common for ignition controls to make several ignition attempts and then lock out for a period of time before trying again.

You probably have more than one issue.

Since the left burner lit but the gas still shut off, it may be that the flame sensor isn't reliably detecting the flame. I'd take the flame sensor out and brush it off with a wire brush or do a little polishing with a piece of emery cloth or fine sandpaper to clean off the invisible oxides that can prevent the flames from being detected.

All the burners should ignite every time. The leading cause for unreliable ignition is dirty burners, especially the carryover ports that carry the flames from burner to burner. The burners should be taken out, inspected for any detrioration and cleaned with a wire brush.

There might be other issues, but I'd do these two things and then try again. It might well solve your problem, and if not you've done the ordinary maintenance that needs to be done anyway.
 
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Old 11-14-11, 03:37 PM
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Thanks for reply Seatle,
I misled you a bit with my wording. Left burner never fired. Was describing where and what sensor did. Typically, when problem occurs, no burners fire after glow. But one time, I saw what started off like a good fire up. After bout 10 seconds of glow, burners started firing off in order, right to left. But half way through, they all stopped. Like gas was shutoff, or stalled through the sequence. I only caught that once, and now I only ever see none of the burners lite after glow. Looks like no gas ever gets there. Is there a way to verify gas flow? I'll start putting my hand on gas switch and listen and feel for a change of state. Is 10 seconds of glow before gas seem right?
 
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Old 11-15-11, 07:39 AM
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SeattlePioneer, I will take burners out this week end and clean 'em. I've only been in house a year, was a foreclosure purchase, so house was neglected for a little while. What other good idea maintenance things should I do to prepare for winter? I am pretty handy guy, so no worries about my capabilities, but never worked on furnace before. I'll try not to bore you with dumb questions... Thanks again!
 
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