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Furnace pro's...a bit of help? #3001222
01/02/22 05:41 PM
01/02/22 05:41 PM
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St. Louis, Missouri area
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My HVAC setup is tanked propane (under 35F), and heat pump (over 35F). Trane XV90 furnace. About 12 years old.

Today, the heating (its about 20F outside) started blowing cold air. When I switch off the system, wait a bit,, and turn back on...it will heat for about ten minutes, then back to blowing cold air.

Of course I suspect the "flame sensor" but cannot find one behind the panel. The burners are behind a cased metal box at the top of the unit. There are several couplings going into it (the burner box). One I know is the "temp trip limit switch", the other I don''t know. But they both have two wires going to them. Flame sensor is only supposed to have one.

THere are three screws to the burner box, but I have not (yet) removed them because I don't see a "single wire" going in (that would lead me to suggest there is a flame sensor inside).

There are stickers around the system stated it has been "modified" for this particular propane setup, so I don't know if that makes my "system guts" different from most.

I've Amazon ordered an exact "flame sensor" and "temp" limit switch. As stated tho, I have no idea where the flame existing flame sensor is. Or does the temp limit switch work as such?

Any thoughts out there are much appreciated! wave

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001271
01/02/22 07:34 PM
01/02/22 07:34 PM
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I'm certainly no HVAC pro, but I had a similar problem a couple months ago.
2-year-old furnace on NG, sometimes no heat.
The big clue was a stove (also NG) that was hard to light.
Turned out to be the gas valve @ the meter - about $500 to have replaced.

Re: Furnace pro's...a bit of help? [Re: topside] #3001285
01/02/22 07:59 PM
01/02/22 07:59 PM
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Stanton Online content
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Quote
"flame sensor"


Go on YouTube and type in your furnace model and "flame sensor" and you'll find what you're looking for. Actually I think its more of a gas flow sensor than a flame sensor. Either way, you'll find what you need on YouTube.

Last edited by Stanton; 01/02/22 08:00 PM.
Re: Furnace pro's...a bit of help? [Re: Stanton] #3001334
01/02/22 10:45 PM
01/02/22 10:45 PM
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Powerflow Offline
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The flame sensor in my 25 y/o gas furnace craps out roughly once a year. Each time, I remove the sensor and clean it with a Scotchbrite pad. That seems to be doing the trick.

Re: Furnace pro's...a bit of help? [Re: Powerflow] #3001340
01/02/22 11:05 PM
01/02/22 11:05 PM
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Crook County, ILL
Mastershake340 Offline
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By flame sensor do you mean the thermocouple?

Re: Furnace pro's...a bit of help? [Re: Powerflow] #3001343
01/02/22 11:06 PM
01/02/22 11:06 PM
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Originally Posted by Powerflow
The flame sensor in my 25 y/o gas furnace craps out roughly once a year. Each time, I remove the sensor and clean it with a Scotchbrite pad. That seems to be doing the trick.


You might want to have a pro take a look at that, seems your might be generating soot and that's an issue.

Re: Furnace pro's...a bit of help? [Re: Sniper] #3001363
01/03/22 06:10 AM
01/03/22 06:10 AM
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upstate western ny
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Pretty sure theres a flame sensor in the model
youre talking about .
It would be retained by a 1/4” sheetmetal screw
On left hand side of burners

What error code ( blinks ) are you getting ?
Its on the circuit board , lower panel of furnace.
Should might be a sight glass on lower panel .

If not youll have to remove lower panel
Rig safety switch to close so you can see the board with panel off - and wait for the furnace
to go through it sequence to observe error code .

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001364
01/03/22 06:17 AM
01/03/22 06:17 AM
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upstate western ny
sogtx Offline
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I dont think you need to remove top panel to access fs
But does your furnace look like this ?

Use electric tape to close switch temporarily
Wrap it around a couple times to depress switch

79424D50-40AD-4BD1-BD7B-9928D7829CEE.jpeg
Re: Furnace pro's...a bit of help? [Re: sogtx] #3001365
01/03/22 06:19 AM
01/03/22 06:19 AM
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upstate western ny
sogtx Offline
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See arrow for fs location

F7516798-F14D-4992-BE86-9950A778F853.jpeg
Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001370
01/03/22 07:45 AM
01/03/22 07:45 AM
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USA
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360view Offline
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Some furnaces use the ignitor as a flame sensor.
After the ignitor cools down after getting white hot from alternating current,
the furnace controller looks for a tiny direct current flowing from the “grounded” hot burner metal frame to the ignitor.

Troubleshooting this design of “flame sensor” can be VERY challenging as you need an electrical meter able to read micro amps of direct current.
Soot buildup and corrosion can both mess up proper operation.

Some “universal” furnace control computers like the Carbide 50E47-843 from Emerson allow you to use either type of flame sensor, or convert one to another.

Re: Furnace pro's...a bit of help? [Re: Mastershake340] #3001371
01/03/22 07:58 AM
01/03/22 07:58 AM
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St. Louis, Missouri area
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Originally Posted by Mastershake340
By flame sensor do you mean the thermocouple?


This is the part I can’t find behind the furnace panels:

Trane SEN01114 Flame Sensor
https://www.amazon.com/dp/B00ECEENH...XG58K7XR3B1EHBS?_encoding=UTF8&psc=1

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001381
01/03/22 08:39 AM
01/03/22 08:39 AM
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St. Louis, Missouri area
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Thanks all! Your input is truly appreciated.

The panel safety switch was already zip tied down (by some tech, I guess).

Light code is showing 21 green, to one red.

Sogtx, pics much appreciated....

Your arrow appears to be pointed to the limit switch (see my pic for reference). It has two wire leads going to it (not one, as a flame sensor would have). It appears slightly offset in my pic because the two holding screws are removed while I examine all this.

https://www.amazon.com/SWT1612-Trane-Furnace-Replacement-Switch/dp/B00FEM56CG

https://hosting.photobucket.com/images/y175/Cometstorm/IMG_7603(2).HEIC

360view might be right.

I've been all over this thing and just cannot find a flame sensor:

https://www.amazon.com/gp/product/B00ECEENHG/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1


Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001382
01/03/22 09:08 AM
01/03/22 09:08 AM
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St. Louis, Missouri area
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OK, it’s about 7 AM, 54 degrees in the house.

I started it again, and “at the moment” it’s running a nice blue flame (hardly any yellow).

While it’s running, the light code is 40 green to one red.

I’ll advise how it goes.

Thanks all! I fear it will just start blowing cold shortly, but we’ll see).

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001384
01/03/22 09:20 AM
01/03/22 09:20 AM
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On one unit a friend had years ago we were able to keep the furnace from shutting down due to “ignitor flame sensor current too low” by aiming a hair dryer gun at the inlet of the combustion air fan.

This extra air heat apparently raised total flame temperature enough that the tiny DC current increased past the cut off limit.

Re: Furnace pro's...a bit of help? [Re: 360view] #3001392
01/03/22 10:12 AM
01/03/22 10:12 AM
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First comment is about the modified for propane label. The vast majority of gas appliances are set up for natural gas. Propane has about twice the energy of natural gas so the main gas valve AND the igniter both have restrictors in them to allow the use of propane. Otherwise you'd burn the appliance up. As to finding the igniter, follow the gas piping from the discharge of the gas valve. It leads to the burners and the igniter will be in the same location as the burners. Good luck.


"We live in a time when intelligent people are being silenced so that stupid people won't be offended".
Re: Furnace pro's...a bit of help? [Re: Powerflow] #3001516
01/03/22 02:27 PM
01/03/22 02:27 PM
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Originally Posted by Powerflow
The flame sensor in my 25 y/o gas furnace craps out roughly once a year. Each time, I remove the sensor and clean it with a Scotchbrite pad. That seems to be doing the trick.


Yup. Have had to do that about every other year on my Rheem house furnace

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001715
01/03/22 07:30 PM
01/03/22 07:30 PM
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St. Louis, Missouri area
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Originally Posted by Cometstorm
OK, it’s about 7 AM, 54 workdegrees in the house.

I started it again, and “at the moment” it’s running a nice blue flame (hardly any yellow).

While it’s running, the light code is 40 green to one red.

I’ll advise how it goes.

Thanks all! I fear it will just start blowing cold shortly, but we’ll see).


Update: It’s now 5:30 pm, system has been holding at 72 F all day, and cycling to keep it there.

Dang furnace gremlins! hammer

All I can do is keep an eye on it!

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001857
01/04/22 07:09 AM
01/04/22 07:09 AM
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Two big “ifs”

If you indeed have a system where the Ignitor doubles as the flame sensor,
and
If some of the tiny DC current is going astray due to a short circuit made by electrically conductive soot/dust/corrosion/cracked insulation
then:
changing air humidity will affect how much of the current goes astray

Higher Humidity = problem appears

Low Humidity = problem less likely

You are a braver man than I
if you take a tiny artist’s paint brush,
dampen it with distilled water,
and “paint” suspected trouble spots.

I would wait until warm weather,
or until I had borrowed enough portable electric heaters to keep the house warm.


Re: Furnace pro's...a bit of help? [Re: 360view] #3001896
01/04/22 10:46 AM
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Thanks 360! up

It’s now 9 AM the next day.

All has been perfect for the past 24 hours (knock on wood). Actually had to back the propane heat down to 68 a few minute ago.

Aside from removing the panels, the only thing I did was remove this, then re-installed it. I didn’t even disconnect the two wires.

C340366P02 - American Standard OEM Furnace 3" Replacement Limit Switch https://www.amazon.com/dp/B00FEM579...K3TA6YAMKT3SBMA?_encoding=UTF8&psc=1

I doubt this part is an issue. From what I’ve read, it’s failure symptoms are cold air, and 24/7 can operation.

My fan is now cycling, as is the whole system.

But I have a new one on order anyway.

If I have another issue, and replacing it doesn’t help… then it’s service tech time.

But all perfect for now, and panels back in place.

Re: Furnace pro's...a bit of help? [Re: Cometstorm] #3001923
01/04/22 12:09 PM
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Have you checked/cleaned all the condensate lines? Your furnace creates condensate (water) while operating. After many years of use, some of the drain lines can become plugged/restricted to the point it causes intermittent failure. It can be a pain and time consuming to clean all the lines and associated parts but sometimes it is all it takes to restore proper operation of the furnace.

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