Furnace works, but not always produces heat

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Old 01-03-08, 04:41 PM
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Furnace works, but not always produces heat

Hello, everybody and Happy New Year

I am a complete newbie, so please help me with the problem.

I have approximately 7 y/o Trane electronic ignition gas furnace model TUE100A936K3. It worked perfectly until recently. Now it produces heat for some time up to the preset temperature after it is turned on using the switch on the wall. All 3 air pipes coming in/out get warm or hot. After some time, it stops delivering heat to the room, and the biggest air pipe coming to the side of the furnace gets cold. Two other pipes are still warm or hot. I can see gas happily burning inside. Air delivered to the bathroom on the first floor is warm as it should be. At this point I can turn the furnace off, since it is pretty much useless. Manipulating thermostat does not help. After some time it starts emitting buzzing sounds, and sometimes I felt slight smell. But not always.

Could you please help me. If more information is necessary, I will be happy to provide it.

Thank you for your help.
Dmitry
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Old 01-03-08, 04:55 PM
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Originally Posted by dimame View Post
Hello, everybody and Happy New Year

I am a complete newbie, so please help me with the problem.

I have approximately 7 y/o Trane electronic ignition gas furnace model TUE100A936K3. It worked perfectly until recently. Now it produces heat for some time up to the preset temperature after it is turned on using the switch on the wall. All 3 air pipes coming in/out get warm or hot. After some time, it stops delivering heat to the room, and the biggest air pipe coming to the side of the furnace gets cold. Two other pipes are still warm or hot. I can see gas happily burning inside. Air delivered to the bathroom on the first floor is warm as it should be. At this point I can turn the furnace off, since it is pretty much useless. Manipulating thermostat does not help. After some time it starts emitting buzzing sounds, and sometimes I felt slight smell. But not always.

Could you please help me. If more information is necessary, I will be happy to provide it.

Thank you for your help.
Dmitry
[email protected]

I'm not following your description of what is happening completely. Perhaps you can clarify the following things which aren't clear:


The switch on the wall is the thermostat?

The three pipes are three warm air vents that release warm air into various rooms? Are there more warm air vents? Are all the warm air vents open?


There should be one or more cold air return vents that suck room air in for the furnace to heat. How many of those are there, and are they all fully exposed so that nothing is blocking them other than the grills?


You say that the furnace warms the air to the preset temperature, presumably the temperture set on the thermostat. That's what it's supposed to do. So you'll need to explain again the nature of the problem --- I can't really understand your comments.


The thermostat should switch the furnace on, the burners should turn on and then the fan. The burners and fan should continue to circulate warm air into the room until the thermostat reaches the temeperature for which it's set, and at that point the burners should shut off. The fan should continue to run until the furnace cools off, usually a couple of minutes, and the fan should then shut off.


At what point is your furnace departing from this simplified sequence of operation?
 
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Old 01-03-08, 05:23 PM
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Hi, SeattlePioneer

Thank you for your reply. I apologize for not explaining the problem the right way and will try to do it now.

Switch on the wall is the emergency switch, not the thermostat. I'd happily use some local on/off switch that is not called "emergency", but I couldn't find one on the furnace. The only other option is unplug it.

There are 3 air pipes. 2 connect to the top of the furnace, and one to the side. I suspect that this one is air intake. This one is warm initially, but cools down later.
One pipe connecting to the top is exhaust. This one is always very hot.

After the temperature in the room reaches the preset level, air is no longer delivered to the room. It may maintain this temperature for some time. Eventually it stops, and the temperature declines. This is where sequence of operations breaks down. By looking at the furnace, I can tell that it works, it burns gas, 2 pipes coming to the top are hot/warm, but the intake is cold, although it was warm before. If I leave the furnace to itself (go to work for example), after some time it starts to produce loud buzzing sound and sometime slight smell (not gas). This doesn't sound right to me either. I turn it off using emergency switch, wait some time, turn it on, and the cycle starts all over again.

If there are place that could be open or close, I have not touched them since when the furnace worked flawlessly. So I assume they are in the right position.

I hope that this time I am more clear.
Thank you
 
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Old 01-03-08, 07:10 PM
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The mergency switch is just a power switch to turn 120 VAC power on or off for the furnace. There is no problem using that switch. It's like using a switch to turn power on or off to a light.


Are the three pipes to the furnace that you describe plastic or sheet metal?

You describe the pipe to the side as being an air intake pipe. That suggests to me that these are white PVC plastic, with the 2-3" diameter plastic pipe on the side supplying combustion air and another 2-3" white plastic pipe on top venting the combustion gasses outside. Is that correct?

That would describe a modern, 90% efficient gas furnace in all likelihood. Can you post the manufacturer of the furnace and the model number of the furnace, which should be on a rating plate near the gas burners?

Usually such furnaces do not have three pipes, only two. Is the third one a white plastic pipe about 2-3" in diameter as well?

It sounds like you are describing a problem with the furnace sometimes not lighting and circulating warm air. Sometimes it will, other times it wont and you notice this buzzing noise.


Where is that buzzing coming from ---can you describe the part?
 
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Old 01-03-08, 07:43 PM
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Hi, SeattlePioneer

Please see my answers below

Are the three pipes to the furnace that you describe plastic or sheet metal?
---- Sheet metal. But there are also several thin white plastic ones just like you describe below

You describe the pipe to the side as being an air intake pipe. That suggests to me that these are white PVC plastic, with the 2-3" diameter plastic pipe on the side supplying combustion air and another 2-3" white plastic pipe on top venting the combustion gasses outside. Is that correct?
---- Yes. But I was talking about a big rectangular sheet metal pipe. There is also thermostat for humidifier and electric pump attached.

That would describe a modern, 90% efficient gas furnace in all likelihood. Can you post the manufacturer of the furnace and the model number of the furnace, which should be on a rating plate near the gas burners?
---- Trane electronic ignition gas furnace model TUE100A936K3. I can take a picture, but the site does not allow me to post it.

Usually such furnaces do not have three pipes, only two. Is the third one a white plastic pipe about 2-3" in diameter as well?
---- There are at least 2 of them. But I was talking about big rectangular (2) and round (1 exhaust) pipes.

It sounds like you are describing a problem with the furnace sometimes not lighting and circulating warm air. Sometimes it will, other times it wont and you notice this buzzing noise.
---- I noticed that burners were actually off. This explains why temperature was falling. But the furnace was pretty noisy, so I guess fan was working. Thermostat has it on "auto". This is regular fan noise, not buzzy noise.

Where is that buzzing coming from ---can you describe the part?
---- Unfortunately not. I will try next time I hear it.

Thank you
 
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