Trane XE 78 won't ignite

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Old 04-10-13, 05:20 PM
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Trane XE 78 won't ignite

In Jan I replaced the HSI and this 19 year old furnace worked great for 3 months. This morning, no heat. The blower, HSI and "click" work, but the gas doesn't ignite. I tried powering on and off, no luck. I tried turning off the gas, waiting, turning it again, but no luck. When I replaced the ignitor, I also bought a control board figuring it would eventually go bad, so today I replaced that. Same situation - blower and ignitor come on. Diagnostic light has a fast flash (normal call for heat), I hear the pressure switch click, but no gas ignites. After 3 tries, the system goes into "lockout" (2 flashes).

Other gas appliances in the house work fine.

Suggestions?
 
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Old 04-10-13, 10:19 PM
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Since you replaced the control board the problem isn't there which tells you that the old board is probably ok.

You need to check for 24 VAC on the gas valve wires when the burner should be lighting. If you get 24 VAC then the gas valve has an issue.
 
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Old 04-10-13, 11:13 PM
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Thank you PJmax. I have a new found respect for HVAC techs, working in cramped quarters like my attic, with poor lighting, in really hot or really cold temps, with incomplete flooring, on parts that you have to be a contortionist to reach, that some dumb home owner probably messed up DYI, to name just a few. Kudos to all of you!

My new control board has an error code for the gas valve, but I didn't get that blinking pattern. Could it still be the gas valve?

So, here's my problem. I am a 65 year old single, not-very-agile-in-the attic woman on a fixed income. I'm not knowledgeable about these things, but can usually figure stuff out given enough time. I managed to replace the HSI, clean the ignitor rod and replace the control board by myself.

BUT....Voltage is a mystery to me. I need a "for dummies" explanation. What kind of a voltage test meter do I need? Where are the wires? Under what conditions do I test (while the HSI is glowing?).

If I can ultimately fix it myself, I'd like to. But if I'm going to end up calling a tech, I might as well do that now and save myself another backache.


BTW - I was told by someone else in January on this DYI site based on the behavior of the diagnostic lights that the previous board would need to be replaced, but what's done is done. I was also told that the board probably was on its last legs anyway, because it's almost 20 years old. I kind of like the new board better because it has more codes.

Thank you in advance!
 
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Old 04-11-13, 05:54 PM
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<<
Thank you PJmax. I have a new found respect for HVAC techs, working in cramped quarters like my attic, with poor lighting, in really hot or really cold temps, with incomplete flooring, on parts that you have to be a contortionist to reach, that some dumb home owner probably messed up DYI, to name just a few.

Read more: http://www.doityourself.com/forum/gas-oil-home-heating-furnaces/492910-trane-xe-78-wont-ignite.html#ixzz2QCZqyvqi>>



Ummm. In my experience, homeowners who dump difficult, unpleasant access problems on repairmen are often punished for that one way or another. They may be short changed on quality of maintenance and repairs or gouged on prices.

A decent respect for repairman suggests that you install plywood over the rafters surrounding the furnace and a light with a switch near the access to the attic.

Similar provisions are wise for people with furnaces in crawl spaces.

There were occasions during cold weather and overwhelming levels of demand for repairs when I took a look at unpleasant access offered me by homeowners and just told them "Sorry!" and left.
 
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Old 04-12-13, 09:11 AM
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Update:
I changed out the HSI (which I don't think should have failed in 3 months, but it didn't look pristine) and cleaned the ignition rod (which wasn't visibly dirty).

The first time I turned it on after this, the gas tried to light, but didn't. This is different than what had been happening (it hadn't been trying to light). I tried 2 times after that, and the inducer fan came on, HSI glowed, pressure switch clicked, but the gas didn't even try to ignite.

So, I turned the gas and furnace power off, put the doors back on, and went to bed.

In the morning, I tried once again to get it to start, but checked all the wires for good connections. I don't think any of the connections were bad, but when I tried it, everything worked perfectly and has been doing so for 36 hours.

I'm not sure what I did to make it work again, but am glad it does. If you have guesses or recommendations, please feel free to share. :-)

Thanks for your time!
 
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Old 04-12-13, 09:26 AM
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It sounds like an intermittent wiring connection. Sometimes just removing a plug and then re-inserting it will cause the problem to go away.
Try carefully unplugging wiring on gas valve and reconnect it.
 
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Old 04-12-13, 08:55 PM
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OK, I'll try to identify the right wires tomorrow. Thank you!
 
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Old 04-12-13, 10:21 PM
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Without a multi-meter and knowledge of electrical circuits, there's only so much you can do.

Without taking measurements the best thing someone can do is guess and replace parts which may not be bad.

If it fails, the most cost effective option might be a call a tech.
 
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Old 04-12-13, 10:34 PM
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Muggle - I'm sure you're right. So far, it hasn't failed though. I'm just going to make sure all the connections are secure, and proceed from there. Thanks!
 
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