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Trane XE70 furnace doesn't light.


Nok2007's Avatar
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10-28-07, 12:27 PM   #1 (permalink)  
Trane XE70 furnace doesn't light.

Hi everyone!

My 1987 Trane XE70 gas furnace doesn't come on (Model # TUS100A936A). The spark ignition constantly goes tick..tick..tick..tick even if the thermostat doesn't request heat. The furnace has automatic ignition (auto relight pilot), so I assume it is continuously trying to light the pilot. (I don't see a pilot light.) I had a power outage the other day that might have caused this. The furnace was already on since summer.

I already confirmed that it is not the thermostat. Any ideas what it could be? The relight module or the gas valve?

Does anybody have ideas how I could troubleshoot/diagnose/fix this. It's getting pretty cold here.

Thanks!

Here are some pictures of my furnace:

The furnace:


The gas valve:


The relight box:


The tag:

 
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Jay11J's Avatar
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10-28-07, 04:52 PM   #2 (permalink)  
Sounds like you got a bad Auto Pilot control (white one). This should only light the pilot when there is call for heat.

What happens when you turn on the t-stat to call for heat?

 
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10-28-07, 08:53 PM   #3 (permalink)  
Posted By: Jay11J Sounds like you got a bad Auto Pilot control (white one). This should only light the pilot when there is call for heat.

What happens when you turn on the t-stat to call for heat?
Thanks for your reply! You're right, my assumption was wrong.

It seems to be the wiring rather than the control: I just figured out that if I press slightly on the 5 pin connector on the gas valve, the furnace fires up correctly. With pressure, it stops ticking when there is no call for heat by the thermostat (to answer your question, it ticked as well when there is a call for heat -- just more quickly at about twice the rate).

Should I just rewire that thing from scratch?

 
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10-28-07, 09:02 PM   #4 (permalink)  
The 5 pins?? you mean the wires connection on the gas valve?

If so, I don't recall if this pops off or not.. if it does, make sure all the termals are clean.

 
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10-29-07, 12:58 PM   #5 (permalink)  
Great photos! Any chance you can post the wiring diagram?

That system uses a mercury flame sensing switch that has cold and hot positions. Basically, on a call for heat, the sparker starts and the pilot burner gets gas. The pilot flame warms up the mercury sensng switch which changes position from cold to hot and allows gas to go to the main burner. There is an internal pressure switch inside that gas valve which keeps the pilot on once the flame sensing switch goes to it's hot position. If the pressure switch goes South, you have to replace the gas valve. Some models also had a resistor in the flame sensing circuit. I'm not sure if those parts are still available. I'm thinking there is an upgrade to a more modern ignition system, but not 100% sure. it's been a while since i have serviced one of these systems. I sure would like to see that schematic if possible. Concerning the sparker ticking when the t-stat is not calling for heat. Did you install a digital thermostat? Many of them use triac switches which have a small current flow thru them even when not activated.


Last edited by daddyjohn; 10-29-07 at 01:06 PM. Reason: add txt
 
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01-15-09, 01:20 PM   #6 (permalink)  
trane xe90

i have a similar problem. when i need heat i have to turn system off then back on several times before the pilot will come on and stay lit. when it does heat it will work fine until the room reaches temperature on thermostat, at that point furnance and i assume pilot shuts off, when room falls below temperature on thermostat, unit comes back on but blows cold air. whats the deal???

 
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01-15-09, 03:15 PM   #7 (permalink)  
Hey Jerry----

It rapidly becomes confusing to deal with two problems on one thread. If you start a new thread, you'll probably get some help.

 
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01-15-09, 06:46 PM   #8 (permalink)  
Hey daddy---

Very good of you to catch the mercury safety switch there. That slid right past me until I saw your post. I've never seen a mercury safety system like that on that style of gas valve.

I probably have a 3 pin and 4 pin Mercury safety switch kicking around someplace in my cold inventory, though.


But anyway, getting back to nok, my undestanding is that he has a spark but no pilot lighting. Is there gas coming from the pailot burner or no gas at all?

If there is gas but it's not lighting, the pilot burner and pilot orifice probably need to be cleaned.

If no gas, that could be lack of a gas supply, a gas valve turned off, a burned out gas valve relay or perhaps something else.

If it were me, I'd turn the furnace off and take the pilot tubing out of the gas valve and turn the furnace on to see if gas for the pilot is coming out.

 
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01-06-11, 05:18 AM   #9 (permalink)  
I've had the same *&^* problem with my Trane XE70 for 20+ years. After my Larkin furnace man ripped me off 5 times replacing relays and costing me $100's of dollar...I figured the problem out myself. On your second picture from the top...you see that clear "nipple-looking thing"?...Try tapping or moving it...it makes my furnace quit ticking immediately and the furnace comes on. I don't know if that clear nipple is only holding two wires together (like adjoining two common wires) or if it is covering some soldered connection. I would like to take the nipple off and retwist it on to make a better connection, but I am afraid I might break something by trying that. Write me back if this works for you or if you find out anything more ([email protected]). I'd also like to know how & where to oil this furnace, as I am tired of paying $60 service calls (plus, what kind of oil to use.)
Nancy

 
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02-22-11, 11:26 PM   #10 (permalink)  
Sorry to (re)bump this thread from the dead, but I'm having this exact problem with my XE70. I've determined that my issue is with the plug-setup as well. I originally thought my issue was in the clear plug shown in the photo labeled "gas valve", but i think it's actually the female end that the plug goes into. I cut off the wire crimp as referenced in the post above mine, and re-soldered the connections. It didn't do anything.
Tonight, I de-pinned all the wires from the plug itself, and re-bent the pins to make sure they were making contact when plugged in. It didn't make a difference (except making the plug fit a bit tighter).

I can jam a nail between the plug and the little block behind it - if i can keep the pressure on the plug at the right angle, the ignitor will light. If not, it will just keep clicking...

It's going to be cold up here the rest of the week, and it would be way cool if i could get this fixed (or at least find some new parts to fix it) so my girlfriend stops complaining.

Thanks ahead of time.

 
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02-26-11, 09:30 AM   #11 (permalink)  
Trane XE 70 parts

Hello , Were you able to get the parts you needed to repair the valve -igniter assy?? I have the excate samer problem! Tick Tick Tick !! no lighting of the furnace , the problem does appear to be in the 5 wire plug , and pressure to one side will make it work for awile ! and I have cleaned and recrimped the wire ends !! still same prob??
Any help would be great !! a source for new replacement parts would be screamingly helpful , I have the exact same furnace as shown in the photos provided by nok2007 , I would like to replace the gas valve , just need to find one? Rock


Last edited by rockon26; 02-26-11 at 09:39 AM. Reason: adding
 
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11-14-11, 03:13 PM   #12 (permalink)  
Same Problem Here

Hello, it looks like i am having the same problem here. At first i thought that it was the wires (the three black ones that are twisted together) but as i have been looking at it and reading everyone elses post, i have decided that since several of you have played with the connectors and havent had any luck, that it must be in the male end of the wiring on the mercury switch. I have yet to price one of these, but i almost guarentee that is the problem child of this furnace. If i get this figured out i will be sure to leave another post. Thank you for all that has added to this thread!

 
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11-14-11, 04:16 PM   #13 (permalink)  
Please don't revive an old thread. It becomes confusing, which can be dangerous. I'd suggest you repost on a new thread.

 
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10-14-12, 02:54 PM   #14 (permalink)  
Found source of problem

Thread continued at http://www.doityourself.com/forum/ga...not-light.html


Last edited by robert8; 10-14-12 at 04:14 PM.
 
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