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Still counts as technical-content post.

Originally Posted by slctech

Original thread started in 2013. The original poster hasn't been around since 2019...resurrected thread of sorts.

Replace it. My thinking is you can only sand it so many times. If there's airborne particulate you may want to include one on annual maintenance.

Original thread started in 2013. The original poster hasn't been around since 2019...resurrected thread of sorts.

Make sure the Furnace has a good ground, if it is a carrier you should bend the rod slightly to get it out of the main blue flame.

I'd verify the gas pressure and check for any flame impingement. Should be a nice consistent blue flame.
Also maybe check into getting a new flame sensor this one may have been cleaned too many times.

Is it properly grounded?
Is the face of the burner by the sensor clean/rust free?
Flame sensor wire isn't cracked/shorting anywhere?
Does the sensor wire go through a molex plug on its way to the board? If so check the molex pins for corrosion and a tight fit.
Are you using the OEM sensor and is it properly in the flame?

Originally Posted by TodKarlson

Thanks guys for the discussion. It’s allowed me to figure out that the outside air pipe breaking off does actually matter because air contaminates in my utility room are apparently getting sucked in & dirtying the flame sensing rod (which I clean with a Scotch 3M pad, btw).

As I was reading this I was reflecting on the one of the few times I've gotten in trouble with flame sensors. I was on a call and needed to clean the flame sensor but didn't have my usual method. I grabbed a green kitchen abrasive pad like you describe. It worked for a little while, but I got called back. Serves me right for getting creative and being unprepared. I had fouled the sensor and I had to replace it. I use a brass brush and clean gently. I don't use the brush for anything else.

One other thing. Years ago I worked on a 80% Armstrong furnace that had sealed combustion and an air pipe in from the outside. Weird, right? Point is a 80% option might still exist as a last resort.

I'm with the other guys. Some form of contamination. Laundry chemicals are great for that. Possible solution could be an HRV/ make up air/ etc. if I were you I would start carrying those flame sensors until you solve the problem. A clean new sensor might go longer than one that's been fouled.

Let us know how it plays out.

Mozel tov baby!

Did you say that the clean clothes from the dry cleaner were returned to this building?

Is there residual chemical left on the clothes from the dry cleaning process?

If enough clothing stored there could it accumulate to get into the furnace?

Thanks guys for the discussion. It’s allowed me to figure out that the outside air pipe breaking off does actually matter because air contaminates in my utility room are apparently getting sucked in & dirtying the flame sensing rod.

Frigidaire FG6RA072C-12A


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That is exactly correct tkhvacguy. The other thing that happens is the sand cloth cuts "v" shaped grooves into the rod, creating little valleys that can fill with the sand, leading to an even thicker coating of "glass" on the rod. The more often it gets cleaned with sand cloth, the worse the condition can become. How about a reply to Glenn's request of brand, model and serial?

Have you verified that the furnace is well grounded not only at the flame sensing circuit, but all the way back to the electrical panel?

Jesjen I have always looked at it like this, and also been told when I first started in the field and have always felt it is right but how it has been explained to me is you don't want to use any type of sand cloth on a flame sensor because it will leave sand residue and when sand becomes extremely hot it can become glass and glass in this instance would act as an insulator on the bare metal of the flame sensor and keep it from properly rectifying the flame signal not sure if its completely right but I can see how that would happen


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Glenn thanks for the reply I have spoke with tech support they pretty much said I'm on my own I do believe that it is something in the air just not sure what it is or how do cure it but I wanted to ask on here to see if anyone else may have ran into it and what they did to repair it instead of a monthly bandaid everything has been helpful so far


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I was once told never to use grit cloth on a flame sensor because they use silicone in the manufacturing process to hold the grit on the paper. So then over time as the rod heats up the coating hardens and acts as an insulator and interrupts the flame signal. I'm not sure how true this is but it makes sense.

Do you mind if I ask exactly what brand and model of furnace this is. I ask, because over the years, at times manufacturers have had service bulletins, and changed components for exactly the reasons you have described, which has included flame sensor changes, relocation changes, and ignition module/circuit board changes. Myself or other members here might be able to help you if we have the exact unit you are referring to. If not, have you called the manufacturer tech support to see if they have made changes.

I have a 2 stage Ruud furnace that once a month amber light blink clean it and I comes back in a month later replaced sensor now gonna change the board this is direct vent to outside 12 ft above the ground

could be highly underfired or lack of post purge. this is causing the acids in the flue gas to attack the flame rod at off cycle.

The flame is conductive and the circuit is between the flame rod and the burner. So be sure to clean the metal parts of the burner near the flame rod so you get good current. You should also put a meter in series with the flame rd and see what your getting.

Try reversing hi voltage to the unit , a class i attended claims polarity will cause flame sensor fault .

Gas pressure is 3.48 " wc