Trane XE80 Not Igniting, blowing cold air.


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Old 12-31-07, 09:36 AM
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Trane XE80 Not Igniting, blowing cold air.

As title states, the heater is blowing room temperature air instead of heating as normal. Our first inspection of the led indicator light shows a "Code 4-Thermal protection activated." The fan, and thermostat are operating and fully functional, however, with no heat.

I've found as much information as I could online, but I'm looking for some more detailed explanation and some insight on diagnosing/replacing whatever needs to be done.

Thanks in advance.
 
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Old 12-31-07, 12:13 PM
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The error code is vague. It suggests that the furnace has overheated and shut off on the limit switch. The most common cause of that problem is a plugged filter. Other causes might be return air or warm air ducts that are mostly covered over or closed, a plugged up or damaged duct system, or a fan wheel that's plugged with dirt or debris.


Turning the power to the furnace off for a few seconds, then on again willobably reset the furnace and give another ignition trial. If so, you want to observe the sequence of operation as the furnace heats up over time and observe what is happening in detail.
 
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Old 12-31-07, 08:03 PM
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Xe80?

Is it possible that the unit is actually an XR80 or an XB80 instead of XE80 as reported here?
 
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Old 04-04-10, 09:47 AM
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I am having a similiar problem, if not the same. Upon waking in the morning I found the temp in the house to be much lower than the set temp. Most often when this is the problem the filter is dirty, so I cleaned that and put the filter back in. I noticed when I pulled the filter is was warm and I have never noticed this before. I reset the thermostat, but the ignitors would not turn on and glow. The panel is showing Code 4-Thermal protection activated.

I watched the pattern.

The fan is blowing constantly and after resetting the thermostat the ignitors will not click and glow. The system stays in Code 4-Thermal protection activated for approximately 5 minutes then it goes to normal call for heat, lights and runs for about 1 minute before going back into the code 4 status and the gas shuts off.

This cycle keeps repeating itself.

My thought is I may have a blocked exhaust vent, but am not sure.

Any advise would be greatly appreciated.
 
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Old 04-04-10, 10:04 AM
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The furnace is overheating and shutting off on the high temperature limit switch.


The usual causes for this are a plugged or dirty filter, too many warm air vents closed, return air vents obstructed or something else obstructing the air flow through the furnace, such as damaged warm or return air duct work.
 
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Old 04-04-10, 12:27 PM
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If not from the typical stuff SP mentioned -

Have you found your filter dirty or plugged often? And what kind of filter do you have in there? Depending on the filter, if dust gets by it, it can clog the secondary exchanger or an AC A-coil located above the furnace, if you have centrl air.

If you have a voltmeter you can test to see exactly where in your low voltage safety wiring that the power is lost at. I recently had one where the high limit did not go out (causing yor same symptom), but another safety device on that same circuit went bad: The spill switch(to sense too hot exhaust gas) located on the inducer fan housing went bad, due to not an overheat condition, but corrosion, and went 'open' because of that, causing the furnace to not ignite, and the blower to run all the time.
 
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Old 04-04-10, 12:35 PM
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Good points there as usual, Ecaman.
 
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Old 04-04-10, 01:26 PM
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The filter clogs what I would consider often, every 4-6 weeks I have to remove it to clean it. I do alot of woodwork in the garage. It has the steel mesh one in it.
 
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Old 04-04-10, 04:51 PM
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Oh my! Not good.
You might indeed have some dismantling to do.

To get at the secondary heat exchanger on an upflow high efficiency furnace (if that is what you have) you have to take out the blower. A very easy job with most, as they are held in by 2 screws usually, and then the whole blower housing slides out towards you on two side tracks. And you may have to drop a circuit board box out of the way to do it (that to may be held up in place by 2 screws) - still an easy job, relatively speaking. Then you have to lay on your back and with a light, look up, and you will be looking at the underside of the secondary exchanger fins that might have sawdust partially plugging them.

The incoming return air gets drawn through the filter, and then through the secondary exchanger, and then up past the primary exchangers, and then once up top, it might encounter yet another clogging place - and that is if you have the cold coil of an AC system above the furnace, called an A-coil. They are designed so that all the air has to pass through that coil without getting around it, even in the winter time!. So the coil fins can also clog up and would need to be cleaned.

Accessing this coil can be somewhat challenging sometimes. But they got the coil in there, and usually there is a fairly clean way to get to it, by (if necessary) unscrewing corner screws at the upper main plenum, then carefully separating the sheetmetal at 2 joints(like with putty knives or chisels). I have done this several times, just for the reason stated, and without messing up the sheetmetal/joints. And on some I have found them quite dirty or clogged, and other times not.
 
 

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