Trane XL90 No Gas No Heat :(


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Old 03-03-10, 09:12 PM
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Trane XL90 No Gas No Heat :(

Hello all!!! I'm in desperation mode, the wife wants me to call the HVAC guy, and I'm a DIYer so it pains me to have to do it. Hopefully, y'all can help me out:

TRANE XL90 (1989)
Model: BLU060K942B4

Symptoms: I turn the thermostat to heat/auto. It kicks in, the fan blows cold air. I go the the furnace, and open the cover. I turn off electricity to the unit, then turn back on. The fans kick in, the ceramic heating coil ignites red hot, but the burners do not fire. In my not so professional opinion, seems like there is no gas coming out where the burners are. I take a lighter to the where the gas nozzle is, and I get a tiny little "pilot light", so there is gas coming out, but not enough to ignite fully.

After reading online, possible solutions, please advise:

1. Flame sensor is bad: I don't know why this would be the case b/c there is no flame to sense. I thought it sensed flame AFTER the burners ignited.

2. Bad ignition coil (the cermaic coil that glows red to fire the burners): Seems to work okay to me. Burns red hot.

3. Bad Gas valve (attached to the main gas line, with a manual on/off "knob" with 2 little black boxes on top): Hope this isn't it because it's the most expensive part.

4. Bad control board: I don't know how to test this.

**Please help, I'm hoping it's either #1, or #2, because #3 and #4 look like it's getting expensive plus it's not a DIY type job. Thanks!!!
 
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Old 03-03-10, 09:41 PM
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muliti stage furnaces can also have multiple air pressure switches...check you vents for blockages or water
 
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Old 03-03-10, 09:43 PM
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I'd start by checking to see if you have 24 VAC switching on after the HSI gets hot. If you do, check to see if your gas supply is good and all the valves are turned on. If that's OK, then you have a defective electric gas valve.
 
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Old 03-04-10, 05:15 PM
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Thank you guys, I'll definitely check the blockages and take a voltmeter to it. Hopefully it's just some squirrel living in one of the vents
 
 

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