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Old 10-28-2012, 12:53 PM   #1
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Intermittent no heat on Trane XB


We just started needing a little heat the last few days, after having to use the AC every day a week ago. The first time we used the heat it had a burning dust smell (which we notice every year). Within a few cycles it started blowing cold air. It wouldn't turn off even after the thermostat attempted to turn it off, the fan just kept blowing. Last year this same thing happened within the first few days of using the heater, but only did it one night, then fixed itself.

This year, it seems the probablem isn't going away. A few days ago, I removed the air filter, cleaned the flame sensor, flicked the breaker, and it worked fine. Later that evening, same thing happened, thermostat kicked the furnace on and it blew cold air, but thermostat wouldn't turn it off. I have also vacuumed out the condensate line from the outside with a shop vac and disconnected the flue to try and shake stuff out.

Everytime I go up in the attic to observe, it works fine. This morning, it started to do the same thing. I climbed into the attic and saw the furnace running with no flame. I pulled the cover to check for error codes, and just got a call for heat, but no alarm. Pulling the cover caused the unit to restart and I saw the inducer motor start, the ignitor light, no gas fire, and then the fan motor comes on. I let go of the door switch to check resistance of the sensors, and all were about 2-3 ohms. When I closed the switch again, it fired up and cycled normally.

Can anyone point me in the right direction on what to check? I am competent in electronics.

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Old 10-28-2012, 01:03 PM   #2
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Intermittent no heat on Trane XB


you need to check the diagnostic LED code when it is acting up, but it sounds like a temperature limit is tripping and causing the blower to run constantly.

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Old 10-28-2012, 01:04 PM   #3
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Intermittent no heat on Trane XB


Dirty burners possibly.
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Old 10-28-2012, 01:10 PM   #4
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Intermittent no heat on Trane XB


This morning it was acting up, I pulled the cover to check the LED. When I pull the cover, the LED goes out. It won't light up again unless I push the switch. When I pushed the switch, it was blinking fast without pauses, normal call for heat. There wasn't a trouble code, and fired up fine.

How can I clean the burners, and how would dirt prevent the unit from firing intermittently?
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Old 10-28-2012, 01:10 PM   #5
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Intermittent no heat on Trane XB


Why did you have to remove the cover to check the LED? Doesn't it have a small window to view error codes through the door?

Removing the door will usually reset error codes unless the door switch is taped down, and that would be an unsafe thing to do.

You can mark the location of the LED on the door and then drill a 5/16" self tapping screw into the door to allow viewing of trouble codes if you do not have this window but you have an LED for diagnostics.

What does you meter measure when you touch your leads together? 2 ohms?

If this is an XB80 your evaporator coil is probably dirty. What is the air temperature entering and leaving the furnace? What is the rated heat rise on the furnace nomenclature inside of the furnace burner section?

If this is a 90% furnace I recommend calling a pro to check the secondary heat exchanger.
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Old 10-28-2012, 01:14 PM   #6
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Intermittent no heat on Trane XB


Wow, I need to speed up my typing. I was responding to the first post.
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Old 10-28-2012, 01:17 PM   #7
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Intermittent no heat on Trane XB


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Wow, I need to speed up my typing. I was responding to the first post.
Its just being in Texas your a few hours behind us easterners. LOL
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Old 10-28-2012, 01:18 PM   #8
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Intermittent no heat on Trane XB


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Originally Posted by Waltherjt View Post
This morning it was acting up, I pulled the cover to check the LED. When I pull the cover, the LED goes out. It won't light up again unless I push the switch. When I pushed the switch, it was blinking fast without pauses, normal call for heat. There wasn't a trouble code, and fired up fine.

How can I clean the burners, and how would dirt prevent the unit from firing intermittently?
Would need to disassemble the gas train, and take the burners out.

Dirt interfers with the gas flowing through the burners.
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Old 11-03-2012, 01:02 PM   #9
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Intermittent no heat on Trane XB


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Why did you have to remove the cover to check the LED? Doesn't it have a small window to view error codes through the door?

Removing the door will usually reset error codes unless the door switch is taped down, and that would be an unsafe thing to do.

You can mark the location of the LED on the door and then drill a 5/16" self tapping screw into the door to allow viewing of trouble codes if you do not have this window but you have an LED for diagnostics.

What does you meter measure when you touch your leads together? 2 ohms?

If this is an XB80 your evaporator coil is probably dirty. What is the air temperature entering and leaving the furnace? What is the rated heat rise on the furnace nomenclature inside of the furnace burner section?

If this is a 90% furnace I recommend calling a pro to check the secondary heat exchanger.
It is a Trane XB. There is no mention of 80 or 90 anywhere on the unit. From looking at pictures on the internet, it looks like a standard heat exchanger (not condensing). There was no hole to view the led, but I drilled one. It is flashing twice.

The meter measured 2 ohms with the leads together as well.

I cleaned the dust off the evaporator coil. It wasn't very dusty, but I got what was there.

It seems like the unit is trying to light 3 times, and then throws the code. After that the fan comes on. It won't go off unless I unplug it. Sometimes it fires up normal after power off, sometimes it doesn't.

If there was dirt in the burners still after several uses, wouldn't it only affect the dirty burner and not all 4?
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Old 11-03-2012, 02:15 PM   #10
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Intermittent no heat on Trane XB


Post full model number. Weather its an 80 or 90% is in the model number.

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