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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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I'm having a problem with my Trane xr90 furnace. It seems to

Customer Question

Hi Douglas, I'm having a problem with my Trane xr90 furnace. It seems to start up, and the ignition filament glows, but the gas won't ignite. It did this the past winter, but the problem resolved when I removed the cover of the ignition area. This time that doesn't seem to do it. Any ideas?
Submitted: 1 year ago.
Category: HVAC
Expert:  Tim H. replied 1 year ago.

Hi, I'm Tim, an HVAC expert here to help you resolve your issue. Please provide as much information as you can. Also, I may depend on you to be my "eyes and ears" since I'm not there onsite. At the end of our dialog, when you're satisfied with the answer, you will have a chance to rate my service. Please wait until then. I'm sorry to hear about your issues with your furnace. It sounds like either a bad gas valve or a bad board assuming we have good gas pressure to the furnace. What flash code do you get? Also full model number will help.

Customer: replied 1 year ago.
Hi Tim, it's a Trane txh025a4hpa2, aka Trane xr90. I wasn't getting a code a moment ago, but now it's the three flash pressure switch code. This all happened last winter and somehow resolved itself to work again, though I'm obviously not sure how or why. I went through the same codes and issues and it eventually worked again.
Expert:  Tim H. replied 1 year ago.

Have you checked intake and exhaust pipes for blockage? If not, that will be the first step.

Customer: replied 1 year ago.
There's no blockage that I can see from the outside.
Expert:  Tim H. replied 1 year ago.

Sometimes doesn't take much. Even a leaf getting sucked into the intake pipe can cause an issue.

Customer: replied 1 year ago.
I'll check again. Back in a few moments.
Expert:  Tim H. replied 1 year ago.

OK

Customer: replied 1 year ago.
Not seeing any blockages. Also, after leaving the pressure switch unplugged all day (to take with my looking for a replacement) I came home today to try it again and it didn't give me the pressure switch code, just wouldn't ignite. This was the same issue last winter with no clear problems of blockage then either. It would only work with the cover off the ignition area.
Expert:  Tim H. replied 1 year ago.

Take the intake pipe off the top of the furnace, Usually this is not glued in place.

Customer: replied 1 year ago.
I managed that, which is difficult due to this furnace being mounted on its side and put in a small recess in my basement. Still not seeing blockages. Any idea why the pressure switch would work sporadically as it has been? Why would it get to the stage where the filament would glow but not light, then not work now 30 minutes later?
Expert:  Tim H. replied 1 year ago.

Does it work OK now without the pressure switch code?

Customer: replied 1 year ago.
No, the code is still present. It was just a short time when I got home that it wasn't showing the code and the filament would glow but not light. When it stopped being a pressure switch code issue I sought out help, but now that code is back.
Expert:  Tim H. replied 1 year ago.

Next thing check the pressure switch and pressure switch hoses? Hoses kinked, disconnected? May want to try blowing them out.

Customer: replied 1 year ago.
I tried all that already unfortunately. Hoses are in the same position they were in when it was working. I flushed them with some compressed air when the furnace was off and there didn't seem to be any issues.
Expert:  Tim H. replied 1 year ago.

Check the barbs on the hose end opposite the pressure switch. Barbs clear?? May want to ream them out with a small drill bit.

Customer: replied 1 year ago.
I'm not sure what you mean by barbs?
Expert:  Tim H. replied 1 year ago.

The pressure switch hoses attach to a "barb" both on the pressure switch itself and the other end may go to the inducer motor or collector box. I'd like you to take hose off, check those barbs. I'm not worried about the barbs on the pressure switch itself, just other end.

Expert:  Tim H. replied 1 year ago.

If these check out and inducer motor is running, check the condensate drainage system. Take hoses off, blow through them, check "trap" down in the blower area. Sometimes this will plug up not allowing condensate to drain properly.

Customer: replied 1 year ago.
Ok, those all seem clear. When I took apart the tubing to get the barbs out and then put it back together (after blowing out with compressed air) the pressure switch code stopped, but I'm back to the filament lighting up with no ignition. No codes, just no fire.
Customer: replied 1 year ago.
The drain area seems clear too.
Expert:  Tim H. replied 1 year ago.

Check for voltage to the gas valve when that happens. Get a meter, set to volts AC and check at the top posts of the gas valve for voltage. If the gas is off, but valve has voltage, we may have a bad gas valve.

Customer: replied 1 year ago.
Unfortunately I can't do that, don't have a meter. I think I'm out of luck tonight. How does this work if I try and get back at this issue tomorrow?
Expert:  Tim H. replied 1 year ago.

You need to check all the things I mentioned. If everything checks out and you have the pressure switch code, it may just be a bad pressure switch. I will be tied up until the afternoon on a heat exchanger install, but can always respond back later when I get back. The chat will remain open.

Customer: replied 1 year ago.
Thanks. I'll check back when I can.
Expert:  Tim H. replied 1 year ago.

Sounds good.

Expert:  Tim H. replied 1 year ago.

Were you able to find a voltmeter so we can continue?