Trane gas furnace won't relight


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Old 02-22-15, 05:48 PM
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Trane gas furnace won't relight

First post and i know little about HVAC so bear with me.

We have a Trane XL90 natural gas furnace that has been acting up for a couple weeks. It mostly seems that the furnace will not light when the thermostat tells it to turn on a second time. We tried new batteries to no avail. The unit will essentially run until its target temperature, shut off properly, and then when it comes time to turn back on, everything in the unit turns on but the pilot light (more of a heating bar) doesn't catch as if there's no gas. There is a red light that blinks at constant intervals in the unit when it fails to light, but I can find no manuals that say what this pattern means. The back of the panel only has instructions on how to turn the unit on involving cutting off the gas knob for 5 minutes prior to lighting, which did not help.

If we shut the unit off at the source with the power switch, let it sit for a little while (30 seconds average), and turn it back on, it will light properly. The only exception to this is last night, the flames wouldn't catch and the flames never came on. We dealt with it throughout the night and it worked fine in the morning heating the house from 56 to 75 with no issues. We chose 75 so if it died, we'd have some excess heat to work with to let the system relax. We typically have it at 69 or 70.

We even had a tech came out who cleaned a sensor (wouldn't tell us which) and said it should be fixed. Same issue happened that night, tech came out again, said it's just blowing out cause of the wind. We have had SOME windy days, but last night it was 35F with almost no wind and still wouldn't light.

I unfortunately can't find a real rhyme or reason as to what causes it, but the only somewhat constants are that when we power it off on the unit itself, then back on, it lights properly 95% of the time. Then when the thermostat shuts it off & tries to reactivate it later, the unit will not turn on. It's also hard to troubleshoot because we have to wait the cycle for it to shut off and then back on (I don't want to stress it by turning it on and off a lot). As a reminder the thermostat has new batteries and the filter is only 2 weeks old as we replaced that when issues first started.

Does anyone have any ideas to try? I'll try my best to provide more information as necessary.

Front Cover
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Inside
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Flames Lit & Working
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Old 02-22-15, 06:06 PM
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The blinking light could be the flash code light on the control board. Different numbers of flashes means different things.
Typically, when everything is normal and the furnace is in stand-by (not calling for heat), the LED will flash about once per second. When the call for heat is received, the furnace should go thru it's normal start-up procedure and the LED will flash slightly faster. If the computer senses a problem, the LED will flash a certain number of times per second, with each frequency of flash corresponding to a particular part. If unplugging and replugging it "fixes" the problem, that's resetting the computer and allows it to run until the computer picks up the abnormality again.

Each furnace has a flash code chart inside a cover somewhere. And in the service procedures manual.
 
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Old 02-22-15, 06:38 PM
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It may be in the location highlighted in this picture...


Do you see a model number on your control board (or intermittent pilot module)?
 
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Old 02-22-15, 07:06 PM
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Houston204: It's model # 50e47-060 but simply states that a flashing light needs to refer to the service instructions, which I do not have.

Just tried reactivating it after it was off for about 90 minutes and the flames are not igniting. The lighting rod lights up as I can clearly see a bright red glow and when I hear the "click" that normally precedes the flames kicking on, nothing happens now.

In the interest of full disclosure, I can't guarantee the tech cleaned the flame sensor. He claimed he did, to my wife as I was not at home at the time, and the bill merely states "cleaned miscellaneous" and no more details.
 
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Old 02-22-15, 07:13 PM
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The flame sensor only becomes active AFTER the flame is actually lit. You have a control board, gas valve or wiring in between problem.
 
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Old 02-22-15, 07:23 PM
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Do you get 24 volts to the gas valve after the HSI glows and you hear this click?

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Old 02-23-15, 09:26 AM
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I apologize for my ignorance but how do I go about testing that?
 
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Old 02-23-15, 10:30 AM
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kinda like this but with the meter set to measure 24 volts AC and the 2 wires from the furnace still connected...

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Old 02-23-15, 05:32 PM
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Got a tester and it only has an option for 600 and 200 V measuring so I set it to 200. When the clicks occurred it was registering 24.2-24.3 on the screen. Fire didn't ignite even though it did this morning and then ran all day.
 
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Old 02-23-15, 06:49 PM
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Do you smell gas when it tries to ignite?
 
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Old 02-23-15, 07:07 PM
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There is an odor usually when we try to turn it on. It's a house from the 70's in a musy old basement so it's hard to distinguish. What's really getting me is in the mornings it will light up with no issues and has the past 2 mornings, it just won't relight automatically or even in the evenings after resting for a while.

Will the smell permeate the air or should I take an upclose sniff AFTER I confirm the flames don't light?
 
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Old 02-23-15, 07:08 PM
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You would need to be standing in front of the furnace.
 
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Old 02-23-15, 07:13 PM
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http://www.amazon.com/Rodgers-50E47-...ords=50e47-843

Can you see the spark?
I would try to clean the spark ignitor area (with the power off) before replacing the board. At least that is an inexpensive board since it only handles ignition and the gas valve.
 
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Old 02-24-15, 07:26 AM
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There is no spark. It's more of a red glow that travels towards the inside near the 3 gas pipes. It lit this morning and then went out less than 10 minutes later. The house was at 47 degrees so I've been overridden by the 2 women in the house and had to call for a tech to come out. I'll post his assessment and cost so you can at least tell us if we got a reasonable deal or were ripped off.

If it wasn't 7 degrees with a full week forecast in the teens each night, we could tough it out for that board to arrive, but each night has been getting colder and colder inside.
 
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Old 02-24-15, 03:27 PM
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Tech claimed our motor is bad and he cannot order a new one so he says we have to get a whole new unit since ours is over 20 years old. Cheapest one they have is $4,000. He also claims we can not purchase a motor ourselves as we have to be licensed to buy one & even if we did manage to buy one, they will not install it. Houston, I have a video of it firing this morning, although briefly, I'll send it you this evening so you can see and hear everything firing to gauge if anything sounds off.
 
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Old 02-24-15, 11:04 PM
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Ouch. That is a very high price and a very surprising diagnosis.
 
 

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