# Trane XE 90 pressure switch



## eddie

I have what I have found by searching other forums is a fairly common problem with a Trane XE90 furnace, I get a code when it dose'nt ignite (3flashes of a led) that shows the pressure switch is stuck open. Some times the furnace lites fine with no problem. Other times it will run the exhaust blower and start the igniter and drop out before the gas lites. Sometimes the exhaust blower will run and run and finally it will ignite after many minutes. There seems to be no pattern to it. Suggestions in other forums have been possible water in the system, clogged vent, locked up rotor in the exhaust blower. I have checked all of these with no luck. Since it happens sporatically I am sure it could be hard to determine the cause. I have a friend in the HVAC bussiness and it has him stumped.


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## Aceinstaller

Air switch troubleshooting checlist......

Plugged flue (bird nests, etc.)

improperly sized flue (see installation specs)

plugged pressure switch tube (remove from air switch, and inducer assembly to clear. then take paper clip and clear connection for tube to inducer assembly. replace tube and call for heat.)

lack of combustion air causing negative pressure in utility room (ensure utility room has proper access to cumbustion air required for make and mark of unit.)

improper low voltage readings for proper operation of air switch. (check electric diagram for proper votage, and see if the voltage at the air switch matches.)

improper voltage at inducer motor. (check diagram for proper voltage, check voltage at motor to see if matching.)

dirty inducer blower wheel. (rare occurance, but worth looking into last) Once I found a mouse that made his way all of the way down the flue into the inducer housing.

If all of these checks are passed, then you have a rare occurance of an air switch going bad.(replace it)


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## eddie

Thanks for all your information. I am sure the flue is clear as the exhaust fan puts out a lot of air. I don't know what Trane specifies but the vent I.D. is 2 inchs which matches the exhaust outlet. It is about 35 feet long.The blower motor run freely. and the tube is not plugged up. You can gently blow or suck on the hose and hear the switch click. .I will try to test voltages as you suggest. As I said sometimes it works with no problem and other times it clicks on and off many times before it will finally light. I only recently realized that this was occuring but as I think back I believe it has been happening for several years. Thanks again.
Also the furnavce is in a large basement so combustion air should not be a problem.


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## Aceinstaller

if you blew down the tube into the switch, you might have ruined it.  hence these diaphrams inside the switch are extremely thin and easily broken with too much pressure.  

My recommendation was to clear the connection at the inducer assembly with a paperclip.  But I guess I should have mentioned WARNING DO NOT BLOW INTO OR INSERT FOREIGN OBJECTS INTO PRESSURE SWITCH AS IT IS VERY FRAGILE.

Also, 2" vent piping should be increased to 3" after a specific length which is determined in a vent table that comes with the installation instructions of the furnace.  I can't stand the attitude that a few bad apples in this industry have.("who needs instructions?")  It seems to me that every year there is something different recommended by our manufacturers to perform on a unit for proper operation and efficiency that is overlooked by some installers. 

For a distance of 35 feet, you should replace that 2" flue with a 3".  Having it installed with a 2" pipe for a long period of time put quite a bit of sress on your inducer motor as well as the pressure switch.  After replacing the flue, don't expect these parts to last forever.


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## zander

It sounds a lot like two problems to me.

It could almost anything associated with the drain, flue, inducer motor, pressure switch.

Well step one at this point would be to replace the pressure switch now that you have subject it to pressures it is not designed for.  I would do this mostly for safty reasons.

Has any one used a magnehilic or monometer or electronic monometer to figure out what the pressures in the system are?  This is nessessary because without this information you are guessing away at what the problem may be.  Mabey an educated guess but none the less.

How old is this furnace?  Age tends to point to the most likely part to fail.
Im not super familiar with tranes but some times the pressure switch circuit is tied into the high limit circuit and the fault code covers both issues.
I would check out that flame sensor too.  Easy to do and eliminates it as an issue.  I don't know if that train circuit board has a specific fault code for it.
I would also think about temperaly making it a singe pipe unit.

Worst case senerio is that you have a hole, crack, seperation in your heat exchanger and the switch won't make because the inducer motor can't work against that.  Secondary heat exchanger could also be plugged up.
Someone familiar with condensing furnaces needs to show up with the correct tools.

I can't spell but i can think clearly.


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## Aceinstaller

Yes,

using a monometer would be the most proffesional way to determine if the inducer assembly is pulling enough pressures.

zander,  Have you ever heard of any products vent tables carry 2" pipe for 35'?

I know that that is a undersized flue. period.
and an undersized flue is the biggest reason for this problem.  Just to bring the installation up to specs for it's intended use, I would replace the 2" with 3" and then troubleshoot.


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## zander

Yup, seen plenty of vents that where per manufactures specs 2" and well over 35 feet.  Brand has much to do with it.  A 40,000 btu furnace could have a vent pipe 2" dia and 60 feet equivelant length.
A 120,000 btu furnace probably needs a 3" pipe to be corect per manufactures guidelines regaurdless of the length.
You could spend alot of money and time changing out that flue and it turns out to be nothing to do with the flue.  AND, even though, it may be under sized it could have nothing to do with the issue at hand.
Your going to have to pay someone to trouble shoot it most likely.
I would seek someone out who is willing to stand behind their work.  ie, not charge you for everycall when they can't figure it out.
Let us know what it turns out to be Eddie.
Ive heard Kentucky is high on the DIY hvac and low on the professional.
Could be a conection there.   Good luck


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## eddie

I'm not sure but I think the problem is solved. It has worked OK since Saturday
Feb. 25. I noticed a sag in the vent pipe of about 2 and a half inches in the last 15 feet from where it exited the house. It is run thru a side wall. I mounted the pipe solidly in line with the pitch of the rest of the pipe and the furnace has come on correctly every time. Keeping my fingers crossed. Thanks again to all who gave advice.


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## dave_borchert

eddie said:
			
		

> I have what I have found by searching other forums is a fairly common problem with a Trane XE90 furnace, I get a code when it dose'nt ignite (3flashes of a led) that shows the pressure switch is stuck open. Some times the furnace lites fine with no problem. .....



I temporarily solve this problem by removing the tube connecting to pressure switch to the combustion chamber and poking a wire through to clear out accumulated mineral ash that is obstructing the narrow nipple.  This appears to be a design problem with the furnace, since the HVAC company that installed the furnace is unable to solve it.


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## Aceinstaller

do not stick any foriegn objects into the pressure switch or blow into it either.  only clear the inducer assembly with paper clip.


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## glennjanie

Ah-Ha, a 2-1/2" sag in the flue line. That is a plumging problem on a "condensing" furnace; with that much sag the water had him cut completely off.
Glenn


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## scott

I awoke this morning to a FREEZING house...my furnace had stopped working. The blower kept cycling on for about 30 seconds then off for about a minute.  I investigated to discover the diagnostic light flashed 3 times when the furnace was supposed to be on. A search for "trane xe90 pressure switch" brought me to this thread.

After reading Aceinstaller's checklist that it might be related to my flue (which I doubted), I thought I'd check anyway.  Sure enough, a wasps nest had been created sometime over the summer just inside the 3" PVC pipe on the outside of my house...large enough to block 80-90% of the exhaust air.  How it affected the "pressure switch", I don't know...BUT, removing it solved the problem and my furnace is working again.

Just want to thank everyone here for not only saving me the expense of a service call but the discomfort my family would have experienced while waiting for it (temps hovering around 0C/32F last night).

...off to purchase some wire mesh!

Cheers.


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## Ponte

I also have a Trane XE90 and I've been dealing with this problem for the last month.  I think it is time to replace the pressure switch.  How does one go about doing that?  Is it a DIY fix or does it require bringing someone in?


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## novice

I have a Trane XE 90 furnace which is in the second heating season. I've just recently had the same problem with getting the code flashing 3 times. After having someone not associated with a Trane dealer troubleshoot my furnace, and finding no problem with any of the usual switches or diaphragms, we were at a loss, thinking the problem must be in the circuit board when we discovered the problem. The problem was with a connecter at the upper left hand side of the circuit board not being completley snapped in place on the left side. It had been arching and had finally got to the place where it wasn't able to make contact any longer. It looked as though it had never been completly seated from the factory. It seats on both sides and is fairly robust in it's seating as it took a little effort to get it to snap in completely. After cleaning the contact of both the male and female at the far left side of tne connecter and putting everything back together, I've no other problems and the furnace is working fine. I don't know if this will help anyone, but just thought that I would let everyone know of this possibility.


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## lputnam

Had the same exact problem. Three flashes on the LED (pressure switch problem) . Pulled off the tube on the furnace (not the pressure switch) and there was a clean white spider web completely blocking the hole. I pulled that out with a paperclip and behind it was a dead spider.  Could not see this until removing the tube. All is 100% working again.  Thanks for saving me about $250 in a service call and the replacement of a pressure switch that was indeed working just fine.


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## MrMiz

Ok I know this was posted in 2006 and it's 2009 now but I wanted to toss my 2 cents out cuz this saved me more than $100... oh and bob villa sucks! Bob if your reading this you need to hire ME as your DIY guy. Why because I have absolutely no qualifications and I fixed this myself! Even though your web site thought I needed to spend a lot of money. I can hardly spell yet I fix problems like this. You do not want to get me started on how much I hate Professionals thinking they are the only ones in the world that are capable of working on anything.

Anyway lets break it down.... I had flying ants this last summer. They get into everything. Down exausht vents into tubes that lead to fancy pressure sensing devices. I vacummed up what I could. I pulled off the tube to the sensore and crunched up and cleaned out the dead flying ants. Used a paper clip in the small sensor part as recommend by this web site.. I think I looked at a lot of sites and bingo no more 3 flashing light errors. Furnace kicks on and MrMiz's buns are toasty!

My after thoughts. LEARN basic SAFETY measures and you can do and tinker with anything! Oh yah and this site rocks and you genious out there that give me the info. You rock even harder.... my socks have been rocked.


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## glennjanie

Welcome MrMiz:
We are happy it worked out for you; now you can give advice to anyone with 3 blinks!
BTW, It takes a very narrow minded person to spell a word only one way.
Glenn


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## manofsteel084

All the information is great. Problem is, I have no idea what hoses to pull off and check. Can't find a diagram anywhere. I am getting the three blinking lights and the small box on the black fan is heating up so I shut everything off. Any help with diagrams or "how to".... is GREATLY appreciated.


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## Jimm Two

All this information was very very helpful. I also had this 3 flashing code; I followed the steps recomended here. 
   What i found was on the exhaust out side there was a course screen to prevent birds from getting in, but on the intake there was nothing . 
    Found at the entrance to the furnace ( on the intake side) a wasp nest plugging off the air from comming in. I cleared the intake completely and put a small screen mesh over the opening to allow lots of air but with little or no restriction. Pushed the run program and the furnace was working.  
  Thank you guys for all the help this was great. Jimm


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## Bubba123

Just signed up to the forum to thank everyone for saving me a bunch of money!

On a Trane gas furnace TUE unit we got the same three flashes which indicates the pressure switch.  A/C guy brought out a new unit and still no dice.  We checked all hoses/exhausts and everything looks good.  Read this thread at the same time he is doing all of this. 

At this point he is convinced I need a new board.  

Can we just try to re-seat all connections etc.?

"Sure, he says - might as well try". 

Wouldn't you know... unit comes right on.  We put the old switch back in and e-voila, everything is still working!

A/C guy didn't even charge me for the trip or anything.  (I still tipped him.)

THANKS ALL!!!!!!


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## accokeek89

Remove the hose from the low pressure switch and plug.  The control board will then run the inductor fan at high speed which should cause the high switch to close and allow the ignition phase to begin.  This should allow the furnace to run on high only till you can get a new low switch.


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## Louieg

I have a similar problem.  I have ruled out pressure switch which I have replaced.  Exhaust seems unrestricted outside the house.  There is not enough vacuum for the pressure switch to be activated.  Could this be a heat exchanger problem?


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## NATEHAWK

Hello everyone I'm new to the forum but see this site is very informative. Right now m having he 3 blinking lights error on my Trane XE90. I removed the inducer blower and it spun free no blockage. I also checked outside in the pipes and they looked good also. Now I removed the little rubber hoses starting with the one on front of the pressure switch and the switch spilled out a good amount of water. I take it that's my problem? I let it drain and took off the pressure switch and drained all the remaining water out of it. I'll hook everything back up and see if it work now? What could be the cost of that switch filling with water? I'm putting two and two together and thinking something has to be clogged. What should I check?

Thanks
Nate


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## hvactechfw

NATEHAWK said:


> Hello everyone I'm new to the forum but see this site is very informative. Right now m having he 3 blinking lights error on my Trane XE90. I removed the inducer blower and it spun free no blockage. I also checked outside in the pipes and they looked good also. Now I removed the little rubber hoses starting with the one on front of the pressure switch and the switch spilled out a good amount of water. I take it that's my problem? I let it drain and took off the pressure switch and drained all the remaining water out of it. I'll hook everything back up and see if it work now? What could be the cost of that switch filling with water? I'm putting two and two together and thinking something has to be clogged. What should I check?
> 
> Thanks
> Nate



The switch needs replaced if it was water logged.  Check the drain trap.  Remove it and run water through till all the debris inside is gone.  Also, make sure the drain hoses from the inducer and cold header to the trap are free and clear of debris.  This is what would have allowed water to reach the press. switch.


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## lostpilot28

Hi everyone, I've been dealing with the same problem for a couple years, but it's getting worse.  In the past, the unit would cycle a couple times before igniting and providing heat.  Toward the end of last spring I awoke to a few cold mornings and found that if I pulled the small hose off the front of the pressure switch, I'd hear the 3-clicks and it would start working.  Now it's getting cold again and doing the same thing, so I ordered a new pressure switch.  Same problem!

So, it appears that the front side of the pressure switch isn't getting enough pressure.  What I've noticed with the new pressure switch is that if the draft blower starts, and I'm getting the 3 blinks on the LED panel, I can pull the front pressure switch hose and blow air toward the hole and it will start.  I'm not even touching it, just blowing air at it.  This tells me that the pressure on the back-side of the switch is VERY close to being enough to close the switch.  What could cause the pressure to to be like this?  I've checked all the vent lines, in and out and they appear very clean.  I don't have a sag in the line, so I'm stumped.  Any help is greatly appreciated!

Also, how do you know if the 1.40" WC switch is right for my unit?


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## hvactechfw

Remove and clean the drain trap.


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## lostpilot28

Thanks for that, HVACTech.  I was looking at that thing today, but I didn't see how it could have any effect on the pressure switch.  Can you elaborate a bit?

Update: It took me about 15 minutes to remove, clean and reinstall the trap, then test.  It didn't fix it...still getting the 3 flashes.


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## lostpilot28

lostpilot28 said:


> Thanks for that, HVACTech.  I was looking at that thing today, but I didn't see how it could have any effect on the pressure switch.  Can you elaborate a bit?
> 
> Update: It took me about 15 minutes to remove, clean and reinstall the trap, then test.  It didn't fix it...still getting the 3 flashes.



Also, would a weak draft inducer motor cause this?  My heater is 8 years old and I would think they'd last longer than this.  Is there a way to test or check the motor or impeller (whatever it is) to see if it's good?


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## hvactechfw

the proper way to find out whats going on with the unit is through the use of a dual port manometer or a magnehelic.  These are specialized tools.  You may want to call a pro.  But before you do....  Do you hear water sloshing around in the inducer while it is running?  Follow the pressure hoses back from the switch where it enters the cold end header of the heat exchanger (to the left of the inducer... should be a clearish hose)  make sure that port is free and clear of any debris.... use a piece of wire or a long drill bit and put it through the port to ensure it is clear.  Much beyone that and you will need a pro or some specialized tools.


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## lostpilot28

Thanks again...I've cleaned the hoses to the pressure switch, and I've verified they're not blocked on the header.  There is no water sloshing around in the inducer.  Any further ideas?


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## hvactechfw

blocked intake or exhaust.....  if you remove the burner box door and then fire the furnace does it run?  if so ensure the screen where the intake pipe enters the box is free and clear of any debris and ensure the intake is clear of debris as well....(the hole piping system, not just as far as you can look into the piping.


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## lostpilot28

Alright...here's an update.  I decided to call my heating repair guy.  I wasn't home, but the wife was...he apparently looked inside with a borescope camera and told my wife there was a crack in the heat exchanger and showed her a picture of the inside of my furnace.  She said it looked rusty, which I'd expect to be somewhat normal.

So, he tells my wife it's a replacement heat exchanger (possibly around $400) or an entirely new furnace (possibly around $1,600).  What do you guys think?  Ever heard of a cracked heat exchanger causing this problem?  If so, is it fixable?  Welding, etc.  I didn't know that gas furnaces had heat exchangers.


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## hvactechfw

depending on the vintage of the Trane XE90 furnace you have, it is possible that it is cracked, but on anything within the last 15 years SHOULD be a serpentine style heat exchanger.  I have only seen a trane serpentine style heat exchanger cracked 3 times, so it's unlikely but still possible.  On all heat exchanger failures you should get a second opinion and be home for it!  Most HVAC companies will do these at no charge as it is usually a lead in to a sales call, but I am leary.  can you take a picture of your furnace and post it?  Just so I know the vintage of yours....  or you can post a model and serial number.  Trane usually had a 20yr part warranty on the heat exchanger which provide you the part and you would be responsible for the labor to put it in.  $400 sounds very cheap for the labor.  The American Gas Association ( the authority on furnaces and heat exchangers in America) gives you 2 options ... 1.  replace the heat exchanger  2. replace the furnace.  The price of $1600 sounds outrageously cheap!  Cheap usually means poor installation and less life expectancy from the equipment.


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## lostpilot28

Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today.  I think a 2nd opinion is in order.  I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty.  He said I'd have to pay $100 for shipping and around $300 for labor to install the new one.  Is $400 for this service expensive?  I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger.  Not sure what this guy's hourly rate is, but $400 seems high.

The model number of my XE-90 is TDX100c948c2.


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## paul52446m

lostpilot28 said:


> Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today.  I think a 2nd opinion is in order.  I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty.  He said I'd have to pay $100 for shipping and around $300 for labor to install the new one.  Is $400 for this service expensive?  I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger.  Not sure what this guy's hourly rate is, but $400 seems high.
> 
> The model number of my XE-90 is TDX100c948c2.



Does this price include schooling, overhead, insurance, plus the mans wages?
 Paul


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## hvactechfw

lostpilot28 said:


> Well, I wasn't there to hear everything that he said...so I may need to talk to him on the phone today.  I think a 2nd opinion is in order.  I am the 2nd owner of the home, so I think the heat exchanger has a 20 year warranty.  He said I'd have to pay $100 for shipping and around $300 for labor to install the new one.  Is $400 for this service expensive?  I've read elsewhere that it takes between 2 and 6 hours to replace a heat exchanger.  Not sure what this guy's hourly rate is, but $400 seems high.
> 
> The model number of my XE-90 is TDX100c948c2.


 that price is very cheap in my area.


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## pookie16

I read this thread and I thought I had a similar problem.  I get the three blinking lights every day and need to manually reset the furnace.
I replaced my pressure switch and I still have the problem.  
If I shut the furnace off and turn it on, the furnace will light.
If I squeeze the tube to the switch and release, it will light.
If I take the tube off at the switch and put it back on, it will light. If I even hold it close enough to get some vacuum to the switch it will close and light. 
The furnace is very new and there is no sign of any dirt or moisture anywhere.  
I replaced the switch because it seemed to me that perhaps it was sticking and needed to be opened and then closed again in order for the contact to be made.  Replacing the switch proves it is not the switch.  There is plenty of vacuum to close the switch, so it is nothing between the switch and the inducer.
What else could it be?


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## Furnaceguy59

I've been struggling with the same problem for years. 3 blinking lights, reset the furnace, replaced the pressure switch, checked for leaks, water, air, everything. Just had a repair guy in today. Everything checks out. Good man. As we were winding things down, he mentioned that a strong gust of wind, in just the right direction, could trip the pressure switch and shut down the furnace. There was no hesitation on my part in answering him. "Every time this has happened, there has been a strong wind." He said, instead of removing and replacing the hose from the front of the pressure switch, all I had to do was reset the furnace, meaning, just turn it off and on at the switch. So folks, it's not your pressure switch, it's not water, it's not your heat exchanger, no, it's not the logic board. It's simply one thing, WIND!


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## pookie16

Then I say that is a bad design.  Wind was my first thought as the first time it happened, it was indeed very windy.  Since where I am from, the wind is almost always from the west.  I could see that perhaps wind from an unusual direction could cause this and that is why no problem for the past 4 weeks.  
I guess this means we will never be able to go on vacation again!


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## lostpilot28

Well, no.  Sorry, I don't believe that for a second...unless you put your furnace outside, or very near an opening.  My furnace is as far inside my garage as it can go.  Not affected by wind at all.

But, as a follow up to this thread, I'm STILL trying to get this issue resolved.  My furnace has worked (albeit stubbornly) for the past 3 months (with my occasional intervention).  But I'm sick of it, and so I had the repair guy out again.  We tested several things and are convinced it's the heat exchanger that's cracked.  Using his digital manometer, we found that the pressure differential between the front and the back is only about 1 in/H2o.  It should be much higher, since the pressure switch is rated at 1.4 in/h2o.

Also, and this was interesting, water was building up inside the draft motor fan.  The water tubes were clear, but when we put the pressure gauge on the water trap (where the draft motor drain plugs in) it read about .5 in/h2o positive!  Basically, that pressure was preventing the water from draining out of the draft inducer.  He believes the pressure should've been zero in the water trap, but since it was reading positive pressure, that was most likely from a crack in the heat exchanger.

So, he's ordering one under warranty.  I'll let you guys know what happens.  

BTW, a run down of what has been done so far: replaced the pressure switch and tested the old one (it was good).  Checked the draft inducer inlet and exhaust - both clear.  Aside from those things, what else could cause a "too low" pressure differential?  The draft inducer motor is one and the heat exchanger is the other.  The draft inducer seems to run great, although we couldn't verify if it was running slow.  I don't think it's the draft inducer motor, though.


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## pookie16

Wind gusts on the roof causing back pressure in the flue.  This would not depend on the physical location of the actual furnace.  That is what I meant.  It makes sense to me, and I say it is a bad design in that if the wind caused back pressure, and then the situation is resolved, it should not require manually reseting the furnace.  If I was king, I would change it so that if the furnace is running for several hours in 3 blinks mode, it should reset itself.


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## Furnaceguy59

It shouldn't require resetting the furnace and Trane knows this. And, I think the dealers know it. And, there's nothing they can do about it unless you replace logic boards with updated firmware. I have no way of knowing this but I'm sure either the firmware has been updated and/or the pressure switch is different on newer models. When I get some time, I'm going to prove my, and my tech's theory. I'm going to take my leaf blower outside and blow varying degrees of wind into the exhaust and intake pvc runs to see if I can duplicate a strong gust of wind resulting in a change in pressure on the switch, shutting the furnace down and getting the 3 blinking lights.


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## paul52446m

Any 90+ furnace can be effected by outside air blowing into the stack That is why i don't like venting them through the side wall. I would rather go through the roof. If you have wind problems and you are through the side wall. instead of going straight out, you might want to but a tee so the wind can't blow in. I live in a cold area and when we first started with the 90+ furnaces we were told by the factory how to run the stacks and we had to start changing the way we run stacks right away. I usually run the intake pipe it a vented attic with a 1 foot long screen on it. This way the wind will not bother it as much. If i have to side wall vent, i try to go out where i will not get the prevailing winds. Some times just reducing the stack on the out side will blow the fumes out harder so it will maintain better pressure in the stack and the wind will not bother it as much.  Paul


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## lostpilot28

Just wanted to post a quick update...I finally got my XE90 fixed.  The heat exchanger was replaced, because the old one had a huge crack in the plastic interface part where the exhaust gas exits.    Surprised I'm still alive to tell you about this!  

Anyway, that huge crack was allowing the pressure to normalize between the front and the back burners...when it should've been over 1.5" H2O, it was only around .9".


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## MarkBean

Aceinstaller said:


> plugged pressure switch tube (remove from air switch, and inducer assembly to clear. then take paper clip and clear connection for tube to inducer assembly. replace tube and call for heat.)



THANK YOU! You helped me restore heat to my house just as hurricane Sandy is hurtling towards us. I scanned the internet looking for ways to solve this problem. After over an hour of educating myself on how to troubleshoot/repair I went up into my attic with all a number of tools, WD40 and my voltmeter. The one "tool" that solved the problem was a paper clip. I didn't see any blockages but after removing the tube and then sticking a paper clip in the tiny hole of the blue valve of the pressure switch, I was back in business. 

Now I'm just a bit concerned and want to make sure that I didn't possibly hurt the pressure switch and put it into a permanent on mode by pushing the paper clip in until it stopped. I'd sleep a bit easier if someone could confirm that one can't hurt the switch in this manner.

On another note, I did see some bug carcases behind the glass porthole before the burners. Should I be concerned about them?


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## Bigdog1

I too checked the bottom trap for clogs and dirt. Nothing. Exhaust Fan motor works. No problem with my flue pipes.

Did the old paper clip trick and the furnace is running.

I had to do it a few times because I don't think I was deep enough the first couple times. But I also wanted to be gentle...

It's very windy and I have had this problem before during WIND events...

Piss poor design if you ask me...Nothing keeps the repairman coming back like a Trane.

On a side note my heat exchanger has already been replaced because of a huge crack...and the BLOWER motor too...

The last time I had a 3 flash problem the water trap at the bottom  was clogged...That was my first stop this time...

Thanks guys....:trophy:


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## nealtw

MarkBean and Bigdog1; Sorry I can't offer any insight but welcome and thanx for sharing.


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## Bigdog1

The problem came back. I did the paper clip again and the furnace fired up but it has since shut down again.


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## pookie16

I see I never posted an update. I was working out of town and my wife was shutting the furnace off and restarting it to keep the house warm.  I got a repair man in.  His theory was that if the cycle time was too short, the vacuum in the flue was not dropping enough to let the switch open.  He put a smaller diameter and longer hose to the switch and increased the temperature differential to restart the furnace.  It seemed to work, so he left with some of my cash, but with the guarantee to come back if the problem was not fixed.  A day later, the problem came back.  I was out of town and my wife went back to restarting the furnace manually. Before I got back to town, the problem just went away.  It is now a year later or so and the furnace seems to be working.
I will reiterate the person's comment that said this is a poor design.  I also thought Trane was a good brand when I bought this new furnace.  The old one (FlameMaster) supposedly had a leaky heat exchanger, but it worked for 17 years that way with one belt replacement.  This new one has broken down on two different problems in 3 years.


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## Bigdog1

Well this is interesting.

It stopped working again and went back to three flashes. I did the paperclip thing again a few more times. It would light and shut down. I took the hose off to the presure switch and the furnace fired up and ran like normal. With the hose off now it has been running normal for 24 hours...WITHOUT THE HOSE...


Furnace repair guy is coming this morning...I can't wait to hear what he says about how it's running normally... and flashing no code.


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## pookie16

Bigdog1: that is sort of scary since the purpose of all of this is to assure the house is not filling up with CO.  All the problems we are having to keep us safe and yours works now with the safety devices bypassed.  I will have to say again, poor design.


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## Wuzzat?

Bigdog1 said:


> now it has been running normal for 24 hours...WITHOUT THE HOSE...


Dangerous, from CO & possibly from NG.


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## lostpilot28

Sounds like what I went through.  Basically, with the hose connected, the heater would stop working...pressure in the upper part of the heater was too high, and the pressure switch would (rightfully so) shut it down.  3 flashes of the LED.

Swapped the pressure switch, cleaned EVERYTHING inside and out.  Still only worked (most of the time) with the pressure hose disconnected.  

The Fix:  got a new heat exchanger (under warranty I think - 10 year old XE-90).  The repair guy pulled the old one out and you could see a HUGE crack on the plastic part of the heat exchanger where it mates up to the blower.  The crack was probably 1/4" wide and about 10 inches long.


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## Bigdog1

Well the repairman was stumped for a while....

We changed the pressure switch and it works fine now.

You could hear a tiny rattle in the old pressure switch...maybe something got sucked into it....and one of the hoses had a small piece of something in it.

My heat exchanger had a big crack in it and it ran for a long time like that.

I had a carbon monoxide alarm plugged in right beside the furnace. It kept going off and I unplugged it...  moral of the story...always trust the alarm....but in my defense....it kept saying gas and there was no gas leak...maybe it classified carbon monoxide as a gas...leak


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## Wuzzat?

IIRC correctly there is a min. spacing req'mt between fuel burning appliances and CO detectors.


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## Bigdog1

I built a room that houses my gas furnace, gas water heater, washer & gas dryer.

I had the CO detector plugged in behind the dryer which is right beside the furnace.

Actually I haven't had one in use now for 10 years. 

I think it's time to buy a new one and install it.

One more thing about the furnace pressure switch issues. This same 3 flashes problem happened last year and it always seems to be an issue when we have a heavy WIND event. Wind is not a friend to my furnace operation. 

My heat exchange crack was found in the middle of winter. I had to wait 1 1/2 weeks for the part to come from Texas. Nice....keep all the spare furnace parts in Texas during the winter....which Texas doesn't have much of. Probably 90% of the furnaces sold in the country are in the Northeast. Keep the part down south....

And now about my "furnace room."


Insurance companies claim about 90% of house fires start from gas appliances.....so I installed a sprinkler head in the middle of this room which will cover all of these appliances with water coverage.

I got an old liquid type (has a yellow liquid in it that will start to boil and the glass will break opening the sprinkler) sprinkler head from work.

Just ran a tap off the cold water line running into my room.

I did mention my "sprinkler" system to the insurance company. It should knock off a few dollars in your premium payment and it gives you a greater chance of surviving a fire and saving the house.

This is also where I have to install my new CO detector.


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## Wuzzat?

Bigdog1 said:


> Insurance companies claim about 90% of house fires start from gas appliances


Do they mean:
Given that you have a fire there's a 90% chance it started from a gas appliance?

or

Given that you have a gas appliance there's a 90% chance that it will start a fire?

These two conditional probabilities are seldom the same.  

And, see what the gas appliance makers say about the cause of house fires.  The truth may be in the middle somewhere, or nowhere near what either entity says.


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## Bigdog1

Just having a gas line going into your house is probably enough of a percentage without anything hooked to it.


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## MarkBean

It turns out that the paper clip trick did not solve the problem. The furnace ran for a bit and then had the same code. I tried it again with the same results. I banged on the intake a bit and some more bug carcases dropped down. Not a lot but enough to notice the difference. We were then without power for a week due to Sandy. The furnace has been working fine ever since we got power restored. My guess is that I have/had a partial blockage in the intake. This weekend's project is to take put my shop vac on reverse and try to blow out anything that may be in the intake. After that I'll put in on forward and clean out the carcases. 

Thank you for the information.


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## Danza

I'm in the same boat with my trane xe90. I've had the front side hose disconnected from the vacuum pressure switch (there's 2 hoses, one on each side) for over a year and its been working just fine. But before that and if I reconnect it now it will quite and give me the 3 led flashes.   
My main concer is having that hose unplugged might cause dangerous gas to go into the home?  Second and less of a concern is its working efficient.  
Appreciate any help!


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## Wuzzat?

There might be a Trane Technical Service Bulletin out on this problem.


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## tgriffith

Just wanted to say thanks to everyone for posting all the great info.  I suspect my problem was strong winds as well, since we had them today.  Simply turned the furnace off (using the main switch on the furnace) and back on - no good, but did that again, and it started working again.
Thanks!


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## karasdad

my five year old XR90 is experiencing the same three blinking lights.  It takes about three or four inducer cycles to get it fired up.  The pressure switched was replaced and it ran fine for about a month and then began the three lights began blinking again.  I can pinch the lower hose for about thirty sec to fire it up but it makes me nervous.  My heater guy suggested I call the Trane specialist to look at it.  I did check the intake and exhaust and they are clear (they come out on the side of the house) but on windy days it takes several cycles to get fired.  I cleaned all the hoses and connections.  I disconnected and cleaned the drain hose from the inducer assembly.  I bought a new inductor fan assembly on Amazon, it's weird how they have it in stock, I suspect it's a common replacement item for $250 so I could be prepared for this weeks sub freezing temps.  The Trane guy is coming out tomorrow morning.  I wonder if he will say he never saw this before.


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## pookie16

I have now had to replace the flame sensor after cleaning it no longer helped.  The blower motor gave out, which I believe may have been the starter circuit which caused the motor to heat up and wreck the bushings.  The three light problem went away a week after a guy came out and put on a longer hose to the pressure switch (but initially it did no good.) I am afraid to leave the house for a week for this 3 blink problem that is solved by turning it off and on.  If a person put in a timer switch that shut the furnace off twice a day, it would be much more reliable which means the design is poor.
My furnace is something like 5 years old, replacing a 40 year old furnace that was reliable but some experts claimed had a cracked heat exchanger.


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## lostpilot28

Just an FYI to those of you having problems.  I went through the same basic checks that many of you did...pressure switch, paper clip, check the flu lines to see if they were plugged, etc, etc.  

When you've tried all the basic stuff (I even replaced my pressure switch with a new one (same model for $40 online) and it doesn't fix your issue, it's probably a cracked heat exchanger.  Mine was cracked for over 2 years while I had repair guys out trying to fix it.  In the end, the 20 year warranty covered the exchanger, but not the labor.  I feel fortunate to have that done by a great service guy for $350.  The problem NEVER returned after the heat exchanger was replaced.

The crack was right on the header of the heat exchanger...about 18 inches long and up to 1/4" wide.  Note that the header is plastic.  Go figure.


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## Furnaceguy59

Hello lostpilot28. Congrats on the fix of your cracked heat exchanger. I had a the crack along with thousands of others. Your problem is not solved. The problem is wind. Your Trane will fail to light when the wind comes at a sufficient force "and" direction. When your furnace fails to ignite again, make sure you cycle the power to your furnace at the switch on your furnace, "not" the thermostat.


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## karasdad

Hey lostpilot28, the Trane specialist came over and you are absolutely right, there was a four inch crack in the heat exchanger.  They are replacing it on Friday along with the high limit switch on the top burner and rollout sensor, both of which they think have been exposed to excessive heat from the burners being fed by the air leak.  How does the crack in the heat exchanger affect the inducer draft?  About six or seven hours to replace, will be about $700.  Also need a new upgraded green circuit board because of some intermittent operation.  I bought one on Amazon, has anyone replaced this themselves?  Is it pretty straightforward?  The Trane tech said it was a weak spot in their brand.  also said I need to get another intake vent added because the current ones don't supply enough incoming air for the furnace to breathe and caused it to run too hot, about 6 degrees hotter, doesn't seem like much.  That will be my next project to manage.  Thanks for all your help.


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## karasdad

Well, I spoke too soon.  Dealer called and said the replacement heat exchanger would not be available for 30 days, none in stock anywhere.  Five weeks in the midst of the Seattle winter is a daunting prospect. $3500 for a brand new replacement furnace.  will consider it because I have no choice, but will probably opt for a different brand.


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## lostpilot28

Furnaceguy59 said:


> Hello lostpilot28. Congrats on the fix of your cracked heat exchanger. I had a the crack along with thousands of others. Your problem is not solved. The problem is wind. Your Trane will fail to light when the wind comes at a sufficient force "and" direction. When your furnace fails to ignite again, make sure you cycle the power to your furnace at the switch on your furnace, "not" the thermostat.



Well, I'd love to agree with you, FurnaceGuy...but it most definitely is fixed.  The wind may be an issue for some installations, but it wasn't for mine.  The final proof for me was to see the "before and after" of the digital manometer readings.  The crack was essentially causing the pressure differential to not be significant enough to override the pressure switch.  Makes total sense to me.  Apparently, it made sense to my furnace, too, since it works great now.


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## lostpilot28

karasdad said:


> Well, I spoke too soon.  Dealer called and said the replacement heat exchanger would not be available for 30 days, none in stock anywhere.  Five weeks in the midst of the Seattle winter is a daunting prospect. $3500 for a brand new replacement furnace.  will consider it because I have no choice, but will probably opt for a different brand.



Sorry to hear about that, Karasdad...I had to wait about a week for a replacement heat exchanger.  Hope you get your issue resolved soon.  I'm thinking that Trane has a real issue with the plastic header on the H.E.


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## karasdad

Thanks lostpilot28, I had a builder friend of mine come over to check it out.  He said the Trane XR90 is a single speed unit that runs wide open at 120 ton BTU all the time; it's a basic contractor model for large homes greater than 5000 sq ft.  However, the ducting design I have limits the intake and restricts air flow volume to through the burner causing it to run too hot and cracking the heat exchanger.  Additionally the A/C cooling coil creates additional resistance to the air flow volume which exacerbates the temp situation.  The Trane dealer was coming over to estimate the cost of adding more intake duct tomorrow.  My builder buddy recommended his HVAC contractor who came over and recommended a York Affinity, a multispeed blower with automatic gas throttling and two stage heating, so it can sense the air flow volume and automatically optimize the performance to heat the house to 1/2 degree of the set temp.  It too is a large 120 ton BTU unit but it can operate at lower air volume and also improve the AC performance.  About $4100 installed, no change to ductwork.   Rebuilding the old Trane was going to cost $1400 and five weeks so I scheduled the replacement for end of week.  I am really excited about having good heat again.


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