# Trane XE78



## bmik2729 (Jan 16, 2009)

*continuing saga..*

It ran for 24 hours this time before failing to ignite again. This time I was able to get the controller status: 2 flashes = System Lockout. I think I am going to jumper the air pressure switch closed so as to eliminate it (or prove it) as the culprit. Even though the inducer blower motor is turning could it not be creating enough draft and it is the culprit?


----------



## yuri (Nov 29, 2008)

It is not the pressure switch as the igniter is glowing. You may have a faulty gas valve or circuit board. Gas valves are not DIY projects. I would call a tech and have him check it. He may have to cycle it many times ( I go up to 30) to catch it failing as it is an intermittent problem. Need to SEE it fail. It probably will get worse/more frequent.


----------



## bmik2729 (Jan 16, 2009)

*Ahhh..*

Thanks Yuri....I went back a re-read the sequencing and you're right. The ignitor comes on AFTER the air pressure switch senses airflow. Damn ....I though I might get this fixed myself. I could do the controller but I would not mess with the gas valve. Is there any way to determine which is the culprit without simply replacing one or the other?


----------



## yuri (Nov 29, 2008)

You have to catch the culprit in action/inaction. If you have a voltmeter and understand electricity you can check for 24 volts across the 2 gas valve terminals and have your significant other turn the heat off and on until you catch it being energized with 24 volts and not opening at that time. If it does not get 24 volts then it usually is the board. Most parts changing techs won't spend the time to do that process. No other way to find out unless it stops completely.


----------



## bmik2729 (Jan 16, 2009)

I'll do that ( I am a service mgr for a hi-tech outfit and use meters all the time). Thanks!


----------



## bmik2729 (Jan 16, 2009)

*It's back...*

The system ran flawlessly for about 10 days!:confused1: Then the problem started to occur again..usually once or twice a day (usually in middle of the night).
I noticed though that the circulation fan and the inducer fan are coming non at the same time. The the ignitor comes on and glows hot and then there is an audible click from the gas valve..and it does not ignite. 
I caught it once failing with no 24v to the gas valve....but 99% of the time the voltage is there. Recently I have also seen it ignite but after about 20 seconds the flame goes out and it re-cycles and tries to re-ignite.
I do not think the circulation fan should be coming on until 45 seconds after the burners light. Could this be what is preventing the ignition? (Previously I replaced the thermostat with a LUX TX9100E) (and when this problem started I don't think it was coming on with the inducer fan).

Any thoughts will be appreciated.


----------



## yuri (Nov 29, 2008)

Sounds like the circuit board is faulty. There should be a 45 second delay unless you changed the thermostat and have the switch at the back set to elec (electric heat). The average life of a circuit board is 10 yrs. If your is original it probably is going bad.


----------



## bmik2729 (Jan 16, 2009)

Thanks Yuri.....I did not pay close enough attention when I installed the new thermostat. It was set for electric. The circulator now comes on 45 secs after the burners ignite (when they ignite). 
Now I just have to decide what to do next for my original problem.


----------



## bmik2729 (Jan 16, 2009)

*...the saga continues*

Well...after getting the thermostat setup correctly (Thanks again Yuri)...the furnace worked great for 48+ hours but failed again during the early morning Wednesday. Typically it will ignite when I reset the unit so in these cases the 24v always is at the gas valve. 
One thing I was wondering it seems to be okay if the outside temp is @ 30F or higer (remember it ran okay for a week after it originally started acting up). It got pretty cold again overnight Tuesday and voila it failed again. I checked the exhaust pipe and cannot find any blockages or anything obvious. I also think that a couple of times the flame has gone out after the unit has been on for a while (because I noticed it trying to reignite itself.
I am rapidly approcahing the clinical definition of insanity....doing the same thing over and over but expecting a different result. I've got to start changing parts. 
I am torn between going for the gas valve or the controller. Even if I purchase both parts and replace myself it will likley be less expensive than a service call. Both of which I am confident I can do but would like to hear what others say about a DIY gas valve replacement. It looks only marginally more dificult to do than changing the propane tank on a gas grill. I know I must dope up the threads and check for leaks after re-assembling. Any thoughts?


----------



## yuri (Nov 29, 2008)

The only thing that changes with temp is the density of the outside air and that can affect the draft in the chimney which will in some very rare cases cause a pressure switch to fail to prove. Yours is okay as the igniter glows. If you caught it once with no voltage to the valve then it ain't the valve. The board is safe and relatively easy to change. They fail 95 % of the time, gas valves fail 5% of the time. Those furnaces run with -30 deg F outside air temp where I am.


----------



## JohnH1 (Jan 9, 2009)

What about low gas pressure? It could be at the point of proving sometimes and not igniting on others ecpecelly if it is a 2 stage unit starting on Low fire.

Missed the XE78 deffinitly not a 2 stage unit. But still could be low gas pressure. Like yuri says below time for a Pro.


----------



## yuri (Nov 29, 2008)

That could be. The Carrier TUA's are very bad for that. Only a experienced tech with a manometer would figure that one out and our poster likely would not do that himself. The burners may need removing and cleaning etc. IMPOSSIBLE to see and do what we do over the internet. He seems determined to DIY. May be best to call a experienced Trane tech.


----------



## bmik2729 (Jan 16, 2009)

It is not a two stage burner; single stage only and it's a Trane.
I thought of gas pressure as well but my gas hot water heater is okay. I also have a free standing Napoleon Gas Stove and it is okay as is my stove. And, if it was low gas pressure how would I correct it...and as I live in association of cluster homes all built at the same time wouldn't others be having the same issues?
I thought this is a DIY forum? Yes I am somewhat determined to fix this myself. As I indicated earlier I work in a hi tech industry (very electro-mechanical devices) and feel very comfortable replacing any of the components myself. I would be a bit nervous about the gas valve only because it has to do with gas. 
I have ordered the new controller and should have it tomorrow. I'll likely replace it on Sunday and hope for the best. If anyone has any suggestions or thoughts on installing the White Rodgers 50A55-843 universal controller I would appreciate them.
Thanks for all the sugestions so far.....


----------



## JohnH1 (Jan 9, 2009)

It is a DIY forum but some things are not DIY for people with out the skills and since we do not know you or your skills we can not be putting someone in a potentially dangerious spot. We want to help but we want you safe also. Do you have a manometer? The manifold gas pressure should be 3.2 to 3.5in water colume. And each home will or can have different gas pressures. The furnace has a different type of ignition system that your other appliances so it can react different to gas pressure. Also it may not be gas pressure at all. It is tough to fully diognose a problem over the internet. Dont get upset if you dont like the awnsers you are getting. sometimes it is better to error on the side of caution.


----------



## bmik2729 (Jan 16, 2009)

Whoa! Calm down JohnH1. You've read something into my post that was unintended. I am very much appreciative of the input I am recieving here. I make my living helping people fix things over the phone so I do understand how challenging it can be. You are only as good as the input you receive...I know that. Tha's why some of my posts have been sort of 'wordy' as I've tried to describe what I'm seeing as best I can.
Actually I do have access to a manometer if the truth be told,,,,but as I said I am nervous messing with the gas..(don't want to see my foundation hole on the 6 o'clock news!). 
All I'm looking for is a little guidance and input from folks who know more about this stuff than I do. Yuri's input that 95% of failures are the controller and 5% are the gas valve was invaluable to me. That can only come from experience. That's what I was looking for. If it turns out not to be the controller, I will not be angry at Yuri or anyone here. Worst case I would then have a new controller on my 16 year old furnace....good for another 16 years or so. 
Thanks again.....


----------



## yuri (Nov 29, 2008)

I believe most Pro's don't really want DIYers opening the gas line and changing gas valves and get nervous about that. We have first hand experience with gas that the average DIYer will never have unless by unfortunate accident. Saving $$ is one thing, endangering lives is another. Good luck with the board. Follow the directions exactly if it is a retrofit and if not sure ask here. We can usually dig up some pdf file or figure it out.


----------



## JohnH1 (Jan 9, 2009)

bmik2729 said:


> Whoa! Calm down JohnH1. You've read something into my post that was unintended. I am very much appreciative of the input I am recieving here. I make my living helping people fix things over the phone so I do understand how challenging it can be. You are only as good as the input you receive...I know that.
> Thanks again.....


No Problem here I am just being carefull I did not mean to sound like you were not appreciative. I guess I still need to work on my phrasing. Good at HVAC not so good at grammer.:thumbsup:


----------



## bmik2729 (Jan 16, 2009)

*It's fixed!*

I wanted to bring this saga to a conclusion and perhaps some of this could help others in a similar predicament.
We last left off with me ordering the controller. Well it arrived Saturday but I was still very unsettled or unconvinced that the controller was the real issue. By all accounts everything was cycling as expected except the burners just wouldn't light. One thing that was gnawing at me was the fact that everytime I put my meter probes onto the connections for the gas valve the unit would always fire up. Always. As the week progressed the failure to fire started occurring more frequently and now many times would be very difficult to get going except when I metered the contacts.
Well, to make long story short *the culprit was the terminal block on the gas valve.*  I had made sure it wasn't a wire or lug issue and the external contacts were cleaned well. It appears as though the connection through or from the terminal block to one of the solenoids was intermittent or loose. By the end of the week I could make the problem come and go and even get the burners to go out by pressing lightly on the connections.
As I said I would not do the gas valve myself so I called a professional and he confirmed my diagnosis and replaced the gas valve. (unfortunately he did not have the correct valve for this model so he put a temporary one on until the correct one comes in a couple of days)(he also was skeptical of my diagnosis).
The tech told me he's seen this a few times but that it is unusual. I feel good that I was able to figure it out (the valve was near the top of my list from the beginning) eventually. And maybe it was better that the problem became more readily reproduceable in order too not have to swap a lot of parts to fix it.
Thanks for all the input and add this one to the list of causes of failure to ignite on these units. BTW - Thanks Yuri for the info on the controller installation.:thumbup::thumbup::thumbup:


----------



## yuri (Nov 29, 2008)

Thats the trouble we have with doing service calls over the net. We need to be there to check those visual items that may be the real problem. Glad you got it going. You may need that board soon as it is near the end of its life. The relays in it will eventually act up or fail.:thumbsup:


----------



## wrogalski (Jun 16, 2008)

*XE78 - Same Trouble*

I have the exact same issue with my XE78. I am going to have the value replaced as well. 

Also, I cannot find a parts list for this unit. Does anyone know what part number the Surface Ignitor is?


----------



## kenmac (Feb 26, 2009)

there should be a part # on the ignitor . After market ignitor# probably 41-407 or 41-408.. Try crossing the part # on the ignitor to be sure


----------



## jvegas (Jan 8, 2013)

I am having the same problem with my XE 78. Will try and jump the relays before calling in the pro for the gas valve to make sure that is the issue. Does anyone have a manual on pdf they could send? also, does anyone have the part number for my model # TDD080C966A gas valve? Thanks in advance... j


----------



## jvegas (Jan 8, 2013)

OK, after checking everything I could do, I called in a Trane pro. He came in, wiggled a few wires on the gas valve and the furnace fired up. after 6 more attempts without touching the wires, everything fired up ok. He explained the gas valve was sticking. He said it would get worse and recommended changing it out now. 109 to come out and diagnose. 375 for the new valve and install. The valve for the xe 78 has been discontinued and he has to install another. Then he recommended a full tune up for 175. Thoughts? Thanks....


----------



## Doc Holliday (Mar 12, 2011)

if you want heat then have the work done, simple.


----------



## jvegas (Jan 8, 2013)

Understood Doc, I just wanted to know if something could be done with the wires instead of changing out the whole valve. I turned it on again last night and got no flame. Opened it up, wiggled the wires, closed it up and away it went. If there was a fix for the wires I'm figuring it would be a cheaper fix...


----------



## Doc Holliday (Mar 12, 2011)

I'd like to know if it's a honeywell smart valve or not. those things are death sentences to your furnace, nothing but replacing them can solve the issue of connections not being made at the plugs. 

I've seen the plugs shimmied and rubber band held in place before.


----------



## Doc Holliday (Mar 12, 2011)

bmik2729 said:


> Worst case I would then have a new controller on my 16 year old furnace....good for another 16 years or so.
> Thanks again.....


 I'd expect for the heat exchanger to crack long before another 16 years, an inducer motor to fail, caps to blow, motors going out, etc. 

it happens to furnaces half your's age.


----------

