Trane XL 90 propane furnace - runs once then system lockout


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Old 11-10-17, 10:23 AM
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Trane XL 90 propane furnace - runs once then system lockout

Hi all, hoping someone has some suggestions of what to try here. Last year I replaced the pressure switch and it was golden for the rest of the winter. This year, I've been battling with it. Last month I replaced the flame sensor, the igniter, and the water pump. What typically happens is what I said in the title - It runs once, pushes heat, and the next call for heat, it's in system lockout and blowing cold air into my house. I have a digital thermostat, don't recall the model or whatever off the top of my head, but it seems irrelevant in this case. I do not have a multimeter to test the control board, but I'm not sure that a faulty board would cause something sporadic like this.

The water pump has a long way to travel to the laundry basin, basically across the entire basement. So it starts on the floor, pumps up to the slats, then travels diagonally across the basement above a drop ceiling before pouring into the basin. I wondered if perhaps there was a clog in the drain line, so I used a wet/dry shop vac on both ends, with no change. As I said, it's a long run, so I thought maybe the vac wouldn't be sufficient and bought a 10' hose and am running it into a 5 gallon bucket to test.

So far, from 7am -> 1pm, the furnace has been running properly without getting into system lockout. That said, I've been optimistic before about fixes that haven't been successful in the end, so the question is if the lockout happens again, does anyone have any suggestions of other things to try?

Thanks in advance!
 
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Old 11-10-17, 10:30 AM
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When it fails again..... look thru the sight glass on the blower access door and count the fault code. Once the door is opened.... the code is cleared.
 
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Old 11-10-17, 10:32 AM
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Every time it fails, it's 2 red lights, for system lockout.
 
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Old 11-10-17, 10:40 AM
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That's the final fault code..... lockout. What is needed is the actual fault code. Post the model number for the furnace. That control board may have fault memory. It may say on the sticker on the back of the blower door.

If not.... I'd start by cleaning the fitting on the inducer blower where the pressure switch connects. I would check the vacuum pressure. You won't have that gauge.
 
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Old 11-10-17, 10:43 AM
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TUX2C100A9482AA
64521RN7G

I assume that's model and serial number.
 
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Old 11-10-17, 01:18 PM
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I don't see any kind of fault memory on the board. The back of the casing only has electrical wiring diagram.

About 3:30pm today, the two flashing lights came back on. Power was shut off to the furnace and then the error cleared, so similar behavior as to what I'd been seeing before running the new pipe.
 
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Old 11-10-17, 01:25 PM
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I don't see any memory stored feature either.
When you reset the furnace it comes back up and runs normally ?
We need to find the actual problem fault code. Some times it takes multiple calls for heat and you sitting there watching for a code.

A brief manual.... manual_trane_tux2.pdf
 
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Old 11-10-17, 05:16 PM
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Yeah, we reset it when it locks out, and it works for a cycle. Would it be helpful if I reset it and counted the green flashes or something? I honestly have no idea how to get the real code.
 
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Old 11-10-17, 06:25 PM
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Once the board is reset.... it's in normal mode. As soon as it defaults a red LED flashes the fault code. After the board goes thru three ignition defaults.... it sets the two flash lockout code.
 
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Old 11-10-17, 07:17 PM
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So it went through one cycle, then the next call for heat was lockout. I shut off the power at the switch for about 45 minutes. When I turned it back on, it flashed the two red light pattern 5x, then returned to the normal blinking green with occasional single red flash to indicate normal functioning.
 
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Old 11-10-17, 07:29 PM
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2 flashes - system lockout - retries or recycles exceeded.
System timing: Retries -2 ....... recycles - 10.
60 minute recycle time.

If it's going to lockout on 1 retry..... I'd say the board has a problem.

It should retry twice and during that it should be flashing the code of what caused it to fault. So that means it should light..... if it shuts down it would flash a code like 3 flashes for pressure switch.... start the cycle again and if it detected the fault a second time it would go to lockout. After 60 minutes the board would do a recycle by iteself and start all over. After the 10 cycles it would stay in lockout until a power down was performed.
 
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Old 11-11-17, 08:09 AM
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Would a board issue be that inconsistent? Ihad to reset it twice yesterday between 5 and 10, and since 10 it's been running fine, so the past 13 hours. If It is indeed a board then so be it, I'll buy one and replace it, but it just seems so odd.
 

Last edited by NYSoM; 11-11-17 at 09:54 AM.
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Old 11-11-17, 08:32 AM
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Just reset it, so I have no idea what to think
 
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Old 11-11-17, 08:58 AM
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I don't like just randomly replacing boards but if it won't log a fault code.... there isn't much choice. You can't repair the furnace without knowing what is failing. In your case it appears that nothing is failing but the board.

You can watch functions of the furnace with a meter if you the time.

You'd put a meter in series with the flame sensor rod and monitor the rectification current. If it dropped and the board faulted.... you'd have a flame sensor issue.

You'd put a meter across the pressure switch. If it showed voltage and the board faulted... you have a pressure switch or flue problem.

You'd put a meter across the high heat limit circuit..... if the loop showed voltage and the board faulted.... you have a safety limit problem..... possibly over heating.

This all takes time and patience.
 
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Old 11-11-17, 09:55 AM
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Time is something that is unfortunately in short supply, so maybe a board replacement is just the best option
 

Last edited by NYSoM; 11-11-17 at 10:31 AM.
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Old 11-11-17, 10:07 AM
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Yeah..... replace that bird.
 
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Old 11-11-17, 10:31 AM
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Lol will do. This site is awful on mobile. Can't see what you type without scrolling up over and over
 
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Old 11-11-17, 06:35 PM
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There seems to be a huge discrepancy in prices for control boards. My current model is CNT04677, which appears to have been replaced by the CNT05159 model, which is well over $300. That seems pretty steep. How certain are you that it will fix my problem? hahaha

Any idea if there is an equivalent that might not be quite so pricey?
 
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Old 11-11-17, 07:12 PM
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I'm fairly certain but I make no guarantees. I get my boards from a supplier. A supplier to the trade is not the same as a homeowner buying a board online. I don't have cross reference catalogs for the boards. My supplier does that for me.
 
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Old 11-12-17, 09:42 AM
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Fair enough. I'm looking into best pricing and will update this thread either way
 
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Old 11-12-17, 12:27 PM
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Last time I reset it I had 3 sets of 2 flashes for a total of 6 instead of the previous 10. Does that mean anything to you?

also, thanks for all your time on this. I greatly appreciate it.
 
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Old 11-12-17, 12:36 PM
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I'm not sure what you are saying. If you do a power down and back up there should be no codes blinking.
 
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Old 11-12-17, 01:06 PM
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I shut it down, wait about 5-10 seconds, then turn it back on. It will flash red x number of times in pairs, then stop and go into normal function with the flashing green light.
 
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Old 11-12-17, 06:02 PM
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That is probably the revision of the board.
 
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Old 11-13-17, 04:14 AM
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Its been 10 flashes on restart except that once, which is why i was wondering. Board firmware identification makes sense. Ordered a board yesterday. Delivery by Friday. Again, thanks for your help, and I'll post the results either way.
 
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Old 11-14-17, 06:48 PM
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Just replaced the board and tested. Same error, two flashes, system lockout.
 
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Old 11-14-17, 07:30 PM
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I was just looking around at the furnace for any obvious physical problems. I noticed that the rubber gasket on the burner box looked like this. Could this be causing the problem? Seems like if it were an airflow / pressure / fumes issue it would be more consistent, but if I knew for sure, I wouldn't be asking.
 
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Old 11-15-17, 05:56 AM
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I just ordered a new grommet to replace that. I'm not sure that's going to fix the issue, but it certainly needs to be replaced. Any other suggestions, or should I just give up and call someone at this point, assuming the grommet doesn't fix it?
 
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Old 11-15-17, 09:53 AM
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I don't have anything to add. I'm checking with my forum partner to see if he has any ideas.
 
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Old 11-15-17, 11:08 AM
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Greatly appreciated.

The new grommet will be Friday, so I'll do that Friday night, but beyond that, I'm at a loss. I can start unhooking various hoses and cleaning them. I assume the best bet is just warm water?
 
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Old 11-15-17, 06:07 PM
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Err I meant compressed air. I need to stop getting distracted by my kids when I type here
 
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Old 11-17-17, 03:59 AM
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Vacuumed out the exhaust and intake pipes yesterday and the furnace ran for over 12 hours, but just needed to reset it again. Grommet tonight, but I can't imagine that the grommet is the problem. Any other suggestions from anyone before I bite the bullet and call a company to fix it?
 
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Old 11-17-17, 06:16 AM
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Could it be a high temperature sensor malfunction or something? I'm curious if there's anything left I can do aside from calling someone.
 
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Old 11-17-17, 08:57 PM
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As I mentioned before..... if the board doesn't log a fault code..... the problem is a guess.
 
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Old 11-26-17, 07:15 PM
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Limit

Suspect high limit. Check air filter. Check where the vacuum line attaches to the blower. Use a rod to poke it clear. Crud will usually build there. Visually look at the evaporator coil. Is it clean? Buff the sensor with a green pad.
 
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Old 11-26-17, 07:19 PM
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Troubleshooting without using tools, is like hunting without a weapon. You’ll likely have to Settle for carrion.
 
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Old 12-02-17, 08:16 AM
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So to update all of this:

About 2 weeks ago, I vacuumed the pvc intake and exhaust pipes with a shop vac from outside. After doing that, it ran for 3 days, then required a few restarts due to lockout. Since that 3rd day, it has not locked out a single time. I have mesh grating over the ends of the pipes outside but it seems that something may have still gotten in there and caused an obstruction.

I've been monitoring it closely but this does appear to be the final fix, at least for the time being.

Thanks all for the help, and with all the parts I replaced this year, hopefully I don't need to replace anything next year.
 
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Old 12-09-17, 03:33 PM
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Of course, in the past couple of days, I've needed to reset it 3 times....
 
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Old 12-01-19, 07:59 AM
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I had this same problem this week, and discovered that with the combustion cover on, the flame wasn't propagating to the left-most (farthest from igniter) manifold. this was causing the flame sensor to trip as it wasn't sensing flame. I found this odd that it would work just fine (startup normally) with the combustion cover off, but when I placed the cover back on, it would fail to start. I removed the 4 screws holding the gas manifold off, and adjusted each of the flame guides. Also, checked all the connections to each of the sensors, checked the air intake, cleaned the flame sensor with steel wool lightly, and re-assembled everything. now, it's working perfectly. not sure which of my activities actually fixed it. I also just installed a condensate pump (what you are calling a water pump), so not sure if that has anything to do with it. Also, I fiddled with those two rubber grommets too, thinking they might be causing a pressure issue.

In your case, you might want to try removing the combustion shield (the metal cover with 6 screws, the one that says "WARNING" and has the looking glass). Start the unit and watch for the following sequence: combustion blower comes on for 30-60 seconds, call for heat, igniter starts to glow orange, gas valve opens, each manifold should show blue combustion, check to make sure the one furthest from the igniter is combusting. that is the one that should have the flame sensor in its path. if you aren't getting combustion in that chamber, the flame sensor won't sense flame and will shut the system down. That was the problem I was seeing.
 
 

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