Trane Furnace Issue

[TexasBob]

Uncles furnace won’t stay lit. Exhaust fan comes on, igniter glows. Sometimes it won’t light at all. Most times it lights the top burner and kicks off before the second is fully lit. New flame sensor didn’t make a difference. Control board light doesn’t flash, not sure if led works though. If you let it cycle enough, it will run on occasion. Any HVAC guys have a guess? Ac lost Freon and they have used window units for a few years. They said last year it would cycle a few times before staying lit.


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[thegrouse]

Low gas pressure or plugged orifices?

[Uncle Saggy]

Low gas pressure or plugged orifices?

This
Dirty?


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[Starman]

Last year, at the beginning of the season, my burners would fire up then shut down immediately.

I discovered that one of the burner tubes had a lot of some sort of insect webbing in it.
Cleaned it out, and it fired right up and has worked ever since.

Hopefully it’s a simple solution like that for you.

[TexasBob]

Thanks guys. I’ll get over there and check that out. Keep the ideas coming please


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[critter69]

Dang that sure sounds like a flame sensor. Do you still have the old one ? If so I would try and " sand" it but not with sand paper as the sand will melt and cause failure. Sand it with one of the green scour pads, then put it back in. Maybe you bought a bad one. Check to make sure the other end has a tight connection to the board. And that the sensor sit in the path of the flame. Another thing it could be is the pressure switch, some work on pressure and some on vacume. You can take the hose ( s) of and blow or suck through it and you should be able to hear the switch close and open. Some times it's the tubing that connects them is cracked. Cut just a small piece off each end. If you take the pressure switch off you will find a small " purple" spot on it. Under that glue is an Allen wrench. Turn in makes it more sensitive, out less. ( I think, I may have that back wards). But I would say it's one of those two things. If you find witch way the switch works ( blow, or suck) and you time it right the furnace should light and stay lit as long as you are blowing or sucking. If it does try the Allen wrench on the back or cut the ends of the tubing. Worst case replace pressure switch. But try the flame sensor first , because it's the easiest. Let me know if this helps you, I truly believe it's one of these two things though. If it's a dirty orfice, watch it when it tries to light, flame should go from right to left, with no hesitation. Flame sensor on left side. If it hesitates, flutters, or does not have a constant flame on that sensor, it may be this also, but is less common ( at least here). It's easy on most models to remove the gas valve and the tube that holds the orfices. You can remove the whole orfice ( there will be multiple ones, depending on btu output) a small wrench, or just stick a paper clip in the small holes. You should be able to look down the Venturi tubes at this time and see if there is any thing in them.

[double bogey]

You may need an actual tech for this one. Do not adjust the pressure switch. Sounds like low gas pressure to me, If the fire isn't progressing from the ignitor side of the burners to the flame sensor side. Flame sensor wont make any difference if the flame isn't reaching it.