Trane VX95 sputtering flame

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Old 12-09-18, 06:07 PM
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Trane VX95 sputtering flame

I have the American Standard version of the Trane VX95 furnace (AUH2B08A9V3VB). Its about a year old and acting up. No issues when running in first stage, but in second stage the flame will sputter and pop at times. The flame will even completely sputter out at times, while the rest of the furnace continues to run. You can see it towards the end of this video.
https://youtu.be/gYnRJsbMMXw

When the flame goes out, the rest of the furnace continues to run though the blower speed seems to reduce. The igniter will then light up, starting the flame again and the blower speed goes back to high speed.

The strange this is that the furnace does not throw a fault code

Does anyone know what is going on with my furnace?
 
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Old 12-09-18, 08:31 PM
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It's hard to tell if the furnace is starving for gas or the gas valve is closing when it shouldn't be. Technically that should come up with a flame sense fault unless the thermostat is stopping the call for heat which would explain the "no fault code". If it was a limit issue..... that would also set a fault code.

Is this a new problem ? Has never done it before ?
Probably wouldn't be a bad idea to call the installing company and check with them. I'm wondering if they checked the gas pressures after installation.

I'm not sure what to tell you. I'd check the W1 and W2 thermostat lines at the control board and see if they are going out. The next step would be to check for loss of voltage to the gas valve and then check for running gas manifold gas pressure.
 
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Old 12-10-18, 04:04 PM
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Originally Posted by PJmax View Post
It's hard to tell if the furnace is starving for gas or the gas valve is closing when it shouldn't be. Technically that should come up with a flame sense fault unless the thermostat is stopping the call for heat which would explain the "no fault code". If it was a limit issue..... that would also set a fault code.

Is this a new problem ? Has never done it before ?
Probably wouldn't be a bad idea to call the installing company and check with them. I'm wondering if they checked the gas pressures after installation.

I'm not sure what to tell you. I'd check the W1 and W2 thermostat lines at the control board and see if they are going out. The next step would be to check for loss of voltage to the gas valve and then check for running gas manifold gas pressure.
Thanks for the reply PJmax. It is a new problem for this winter. It not the thermostat because I can see on the zoning panel that it is continuously calling for heat and the furnace shows a fast flashing green light, which indicates that the zoning panel is calling for heat. In addition, the flame sputters out at times, but then regains and continues to burn for a bit longer.

With the issue only happening in second stage, I'm concerned it may be a cracked heat exchanger since the static pressure is much higher during second stage and therefore the air from the within the ducts is blowing out the flame. If I did have a cracked heat exchanger, would it be possible for the furnace to short cycle like it does without throwing a code?
 
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Old 12-10-18, 10:27 PM
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That is not a cracked heat exchanger. That would not even be a likely problem on a one year old Trane unless they dropped the furnace down the cellar stairs but then it would do it from day one.

I can't get a feeling for what the problem is. I watched the video many times. I do notice that some "fan" shuts down when the flame goes out. Is that the draft inducer shutting down ?

If yes..... then it may be a problem control board. Upon a fault.... the inducer doesn't usually stop. It keeps going as well as the main blower if it was already running. The flame going out and the inducer stopping usually mean a problem with the call for heat.
 
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Old 01-06-19, 08:42 AM
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So an update.
An HVAC tech came to look at the furnace, but unfortunately it was running beautifully and could not reproduce the problem. He checked the flame sensor, replaced the filter, blew-out all the drain lines, opened up the inducer motor housing, checked the furnace was level, and checked that the exhaust pipe was pitched. He may have done more, but that was what I noticed. He did mention that he forgot his manometer, so could not check gas pressure.

The next day the furnace is acting up again. What I have figured its the second stage vacuum pressure switch that is knocking out the flame (using a volt meter, 26 volts continuously going into the switch, but on the output side voltage drops every-time the flame sputters and drops completely when flame completely goes out). I bought a manometer and noticed that the vacuum going to the switch (in the manual this is called the "direct vent manifold pressure") bounces all over the place from 0.3 to 0.09 in H2O, but on average hangs around 0.18
.
What is could be causing me to have such low pressures, resulting in my pressure switch being tripped?
 
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Old 02-03-19, 12:38 PM
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I have a very similar problem with my Goodman furnace. Decided to buy a new inducer (mine is 10 years old) since it seems to be making a whining sound.

Did you end up getting your issue fixed?
 
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