Help: Furnace keeps shutting down

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Old 12-01-18, 10:59 AM
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Question Help: Furnace keeps shutting down

I started to have problem similar to the issue I experienced last November with York furnace, which I had a post for it with many details: https://www.doityourself.com/forum/g...t-no-heat.html

Last year I followed PJmax and Houston204's instructions(THANK YOU GUYS!!) and the problem went away after I reseated(unplugged then plugged it back to the board) the harness and it survived the last winter. Starting this winter, it keeps shutting down, I had to go up to the attic and reseated the harness almost every day. Most of the time it worked after I reseated the harness, and it was only good through the night until the next day. One time I noticed after I saw the fire but it shut down after, then I sanded the frame censor. Since sometimes I couldn't see the fire after three ignites before the error code so I would guess the problem is not about the frame sensor. I tried to blow the board as well as the harness, I wouldn't call them dusty at all. I am not sure if I should replace the harness(the wires, which looks good), or I should pay $100 to replace the board... Please advise. THANK YOU!
 
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Old 12-01-18, 12:30 PM
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I see we left off with contact cleaner in the other thread. You can pick up a small can in most home improvement stores. It will say contact cleaner right on the can. It'll be near the other spray oils like WD-40. If you can't find it..... WD-40 should probably work too.

Take the plug out of the control board. Spray just the pins in the plug with the contact cleaner. Use a rag to keep it from dripping everywhere. Put the plug in and pull out several times to clean the pins. If it's still intermittent..... try spraying it again.

If the unit fires and then goes out within 10 seconds..... it's a flame sensor issue. If it stays lit for several minutes or more..... most likely not. Don't forget to check for a fault code.
 
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Old 12-01-18, 06:06 PM
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Originally Posted by PJmax View Post
I see we left off with contact cleaner in the other thread. You can pick up a small can in most home improvement stores. It will say contact cleaner right on the can. It'll be near the other spray oils like WD-40. If you can't find it..... WD-40 should probably work too.

Take the plug out of the control board. Spray just the pins in the plug with the contact cleaner. Use a rag to keep it from dripping everywhere. Put the plug in and pull out several times to clean the pins. If it's still intermittent..... try spraying it again.

If the unit fires and then goes out within 10 seconds..... it's a flame sensor issue. If it stays lit for several minutes or more..... most likely not. Don't forget to check for a fault code.
Thanks PJmax! I got a CRC QD Contact Cleaner from Home Depot, unplugged the harness, sprayed the cleaner, plugged it back, shook a bit slowly, unplugged it, let it try for a few minutes, then repeat this for another time. After I reseated the harness, I powered on the furnace, nothing worked, no sound no flashing LED. Then I turned off furnace, reseated the harness, and powered it back on, the furnace started as normal.
So it looked to me the problem still persists: don't know if it can start next time. I believe I have sprayed enough contact cleaner, so I doubt spraying more may help.

It ran for a while, then stopped, not yet reached the temperature set, with 7 LED flashes(expected). I may still need to replace the flame sensor, even I have sanded it and it looked clean. This looked top be flame sensor problem, however, it can't explain why sometimes the furnace couldn't start at all(not after failure), It could be another issue.

Kind of weird. I suspect the board, but replacing it is hard for me, so many wires.
 
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Old 12-01-18, 10:19 PM
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Seven flashes is the flame sensor circuit..... not the flame sensor itself. The flame sensor is nothing more than a stainless steel rod that MUST be IN the flame. If it's clean..... it's ok. Don't bother replacing it. Make sure it's always in the flame and that end of the burner is lighting and burning correctly.

Here's what I think the problem is...... it's involved in that multi pin plug. The purple wire in that plug is the flame sensor rod. It's probably not a corroded pin but it may be a loose pin or it's where that plug is soldered to the control board. I don't make board recommendations unless I'm fairly certain it's bad.... but that's the way I'm leaning here.
 
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Old 12-03-18, 01:51 AM
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Hi PJmax, you are right, I could kind of confirm the issue was about the harness contact issue(how the harness connect the socket on the control board), through the following experience:

The furnace failed to start, so I went to the attic today, still noticed 7 flashes through the small window. I reseated the harness, tried to power on, nothing happened, just like completely dead. Then I randomly slowly moved some wires of the harness, then I could hear the furnace started. However, the gas valve didn't work after the ignite turned bright, then again I randomly slowly moved some wires of the harness, I heard a click right after that and I saw the fire was on. So definitely some connectivity issue here, and that explains why reseating the harness worked last year, and it worked most of the time recent days. I pulled out the harness a little bit from the connector on the control board(please see the attached picture, there is a gap between the connectors), which looked to be working for 3~4 times today.

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I have tried to use the contact cleaner, what would you suggest if it fails again? Worst case I may have to replace the control board or the harness. Is that right?
 
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Old 12-03-18, 06:14 PM
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You may try using a tiny screwdriver to spread open the male pins on the board connector. Try that before ordering a new board.
 
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Old 12-03-18, 06:24 PM
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You could try that. Go gently and use a thin screwdriver. If the pin splits.... it's shot.
If it's not a pin connection.... that just leaves where the plug is soldered to the board which would mean a new board.
 
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Old 12-03-18, 09:33 PM
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@4135V: I did try spread open the male pins on the board connector yesterday(so you might have noticed the pins in 2nd picture were a bit opened), but it didn't help(don't know why).

@PJmax: What do you mean "it's shot" if the pin splits? Have I done something wrong already, I did spread open the pins as you could see the 2nd picture.
I am quite sure the problem is about the pin connection, because yesterday when I troubleshot, slightly moving the wire did make difference, that triggered the furnace to start, and later ignited.
I am wondering if I can remove the pins from the plastic head of the harness(that is, remove the metal part of the wires out of the plastic head, and connect those metal head of the wires directly to the 10+ pins on the control board.

After I reseated the harness but not tight, hence you can see a small gap between the harness head and the connectors on the board. The furnace has been running well for a day. I will keep my eyes on it.


Thank you!
 
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