Understanding Flame Rectification on Gas Furnaces! Explanation, Testing, Flame Rod, Ground Issues!

[@gregmercil3968]

I was incorrectly taught that the flame rod is a thermocouple and therefore was never really trained on how they actually work and how to test them beyond just checking the microamps they “produce.” This channel is a godsend! Absolutely essential for techs to watch, especially newer ones like myself. I’m going on two years working in this trade. Please keep them coming!

[@TheFoxygrandpa69]

I'm right there with ya

[@jakobrathbun4596]

It’s funny you say this. I was a little confused at first getting into the field for the same reason

[@emmaa427]

Yes he's top-tier technician....we're blessed to learn from his vast knowledge and experience.

[@videos10]

I'm going on into five years.. I'm still learning, and needing memory refresher, Craig knows his stuff into depth !!!! And he is the pioneer of the hvac technicians videos on KZbin

[@davetysdal5442]

Been doing it for 30 years and trying to save my old furnace. $$$$ to replace!

[@robertray4287]

Everyone who watches you teaching should be very happy Great teaching

[@williamserver4332]

I have 23 years experience and just learned a few things. Thanks for the videos

[@michaelrussell3598]

12 years I've been fixing Heaters and I've been checking this all wrong thank God for your videos

[@wayneschneyer8699]

Hello Craig As always,your professional and excellent videos are so valuable to the technician. As a retired veteran of our industry, I learned something watching this great video. Fantastic demonstrations that probably aren’t shown in trade schools, sadly. Your simply an Awesome gift to our industry! Thank you again.

[@jamesfitzsimmons381]

You are a great teacher. Please continue with your videos

[@dentonhess5810]

Excellent trainer. Doesn't get any better than this.

[@justinrogers4465]

Im an HVAC tech and your videos are awesome, thanks for the content!

[@QualityInnEscondido]

thank you very helpfull fixed our water heater after watching this video thank you again.

[@deanmartin1966]

I did not realize the flame sensor had voltage running through it. Learn something new everyday. Great video Craig. Thanks for sharing.

[@joshuaespinoza6331]

I'm definitely buying his books! I'm ready.

[@razzthokhee9802]

Thanks!

[@acservicetechchannel]

Thanks so much!!!

[@maness2112]

Had no idea the flame rod has volts when the furnace has power at all times. The day is not wasted.

[@zachosborne6577]

Good video man. I remember the first old rheem I saw that read micro amps through the igniter, it threw me tor a loop.

[@cliffweinan3907]

Excellent explanation. Low level DC flame sensor signal makes control board sensitive to AC power polarity because neutral is grounded at power panel. This can be issue if furnace unplugged and does not have newer polarized plug / receptacle pair.

[@qzorn4440]

Wow, the most best Furnace system walk around. 😎 Thank you so much. The flame rod circuit is very interesting. May be check the waveform out with an oscilloscope?

[@johnconnor7501]

I will be testing some of these stuff in the field

[@John-dp3ln]

Great video. Can you address why some furnaces won’t run when powered from a stand alone generator (during a power outage). I’ve found that the neutral and ground from the generator must be connected in order for the control board to allow the furnace to operate. This even happened in an older home with knob/tube wiring and no ground. I’ve had this happen on both inverter and conventional generators. Thanks.

[@Redtooth75]

Most likely it is a grounding issue. Flame rectification requires a good ground.

[@techsunsetmech]

Furnaces rely on a proper ground. If you install a furnace in a knob and tube House you will need to provide a proper ground. I recommend running a dedicated circuit in any install to provide proper power to the system. This will also allow a better length of life to your furnace, since most electrical systems are usually riddled with issues. If you're using a generator I would recommend a surge suppressor for the furnace. I have also been putting those in with the newer ECM furnaces.

[@WillieMakeit]

looking forward to the mini split manual

[@jaymz0074]

Excellent video

[@Pennconst101]

Awesome video. Thank you for sharing the experience.

[@acservicetechchannel]

Glad you enjoyed it!

[@martynlewis9020]

Great video. I’m a UK based gas engineer (not the stuff you lot put in your cars, the stuff we power our boilers with, sorry, furnaces with) I haven’t found a trainer in my years working in the industry that can fully explain the rectification process. When you ask them their explanation turns a bit vague part way through and their answer usually contains the words “magic happens” 😂

[@acservicetechchannel]

Ha ha thats not good!!

[@JohnQPublic345]

Years ago, I swore I got zapped by touching the flame rod. Now I know I wasn't just imagining it. Lmao

[@carsonholtorf8233]

How do I tell if the board is bad and not sensing the flame signal?

[@EnjoyCalculus]

amazing video. liked and favorited as usual

[@odaine45]

The best !!! Good video

[@leiwu-z4j]

excellent explaination

[@jamesfitzsimmons381]

Which test leads are they and alligator lead tips you’re using thanks

[@WillieMakeit]

lesson learned thank you very much

[@davetysdal5442]

I'm having a problem with my Nordyne furnace. It's old but the HE is in good condition. Flame rod signal seems to disappear. Getting around 2-3 micro amps then it shuts off. Tried bending the the flame rod and it worked for a while. Just keeps trying to fire. I just removed the GV and burners. Cleaned them up the best I could w/o damaging them. I jumped the ground to the box, but it didn't help. Will check the CB connector next.

[@mark.r8900]

Hi, there are furnaces that doesn't have a dedicated ground from burner box to control board. So in that case how does the uA get back to the board? If the uA is going back to the board on the ground wire. Then what's the uA reading when your meter was in series with the flame rod? Thanks.

[@farashvac]

I believe it uses the spark rod if you have intermittent ignition system

[@seshachary5580]

very educative. thank you

[@harryschrysan3183]

Gotta love when correcting my boss(he has PhD in engineering and is a fully licensed HVAC tech) about the flame sensor having power ALL THE TIME.. He was arguing with me that it's ghost voltage. I just gave up. He has been giving me false info on other stuff too. So hard to deal with this type of situation.

[@GAMESFORUSdotNET]

Can anyone explain why commercial roof top units do not mount the control board inside a weather proof box? Maybe there are certain models that are engineered this way? Great video

[@superbroolyy]

great content

[@jamesletsch775]

Can you make a video about why my furnace fan works in auto but not in the “on” or circulate position. I have a Lennox gas furnace setup with a two zone system.

[@aifrisyad7491]

the ground wire on the burner is attached to the control module or into the gas valve?

[@masteringtheapproach7815]

Great video you really know your information I'm going to subscribe to your channel and I also gave you a thumbs up I'm having major problems with my stuff my meter does not have a ma setting😢

[@scsclassics]

I have a question ? If a inducer motor gasket is bad and has crumbled / fallen apart and pieces fallen out would that cause rollout switch to shut the furnace down ? High limit . Since there is now a gap in where the gasket was .

[@chieuyang3116]

Craig why would the flame rod have 50 to 180 volts and also why such a wide range? The voltage is not needed correct?

[@mitchc1263]

From my understanding the voltage in the sensor and the resistance that the flame creates is how the flame is rectified. Without the voltage there would be no way to detect any kind of signal

[@JohnQPublic345]

The higher voltage is needed for better accuracy. Lower voltage would need a higher current to pass through all those electronics

[@lastchance8142]

The higher voltage overcomes soot deposition and rod clearance if the rod bends slightly over time. Also, gives a higher DC signal current.

[@johnwest7993]

I'm wondering why you don't use the meter's current loop to get the current reading instead of going to the trouble of putting the meter in series. Is the loop too noisy for microamp readings?

[@EurekaRecycler]

excellent, Thank you

[@acservicetechchannel]

Thanks so much!!!

[@waltherherrera67]

Extraordinario muy bien Gracias

[@enduringpromise]

I believe what causes confusion is this idea that the ground is sending a rectified voltage back to the circuit. I believe a better way to understand this circuit is to realize that DC current sensing is happening on the AC wire and not on the ground wire. The ground wire is needed to complete the path back to the circuit board. It is also helpful to understand that the current measured is in DC microamps because the flame is causing the rectification of the AC voltage.

[@Team99-g3x]

So there’s AC And DC current on the same wire? And the Earth/ground wire is required to create the “Loop” to allow this to happen ? So the ground doesn’t carry the dc voltage back to the PCB ? But the AC Wire actually has the DC current and is providing the proof the flame is there with the same wire back to the PCB ?

[@jimbarron8688]

The rectification is a result of the amount of ions in the flame that are received by the flame sensor. The difference in the physical size of the flame sensor compared to the burner face means fewer electrons going back towards the burner, AC converts to DC and thusly rectification results. The signal then travels to the board in micro amps DC. The board requires the micro anp DC signal which can only be a result of the presence of flame to keep the gas valve operational. The flame sensing rod is placed at the burner fartthest from HSI thereby ensuring that all burners have lit proving ignition.

[@aifrisyad7491]

Ground Wire connect to valve and paralleled to module, right?

[@my-yt-inputs2580]

I have a peculiar issue I'm tracking down with my flame sensor. Do you think a bond(ground) is required for flame sensor mount itself? I realize the mount bracket is attached to the ceramic part of the flame sensor so doesn't seem important. But in my case and in my troubleshooting my issue I have found that wirebrushing the flame sensor mount bracket where it makes contact with the unit frame seems to have solved my issue. So that has me curious. I am waiting for an OEM replacement flame sensor to arrive to test out a new sensor. My unit was short cycling but instead of shutting off in like 3 seconds for a bad flame sensor it would run 10-15 seconds before shutting off then immediately recycling the whole inducer, flame, etc cycle.

[@danlearned6199]

I've watched dozens of videos on the operation and failure modes/correction of flame burner flame rods yet...NO A SINGLE ONE ADDRESSES OLDER FURNACES THAT DO NOT HAVE A FLAME ROD. On older Payne, Day & Night, Bryant and others use according to the schematic a "Safety Pilot (Flame Sensing) unit. Does this serve a similar purpose in a different manner?? How do you check/diagnose one?? This appears to be a part of the Pilot Burner Safety Switch assembly, now only available from Robt. Shaw p/n 1830-620, Can you PLEASE address this????

[@Pennconst101]

I just had flame rectification kick my butt for two hours on a hanging heater. The ground wire was a spade, and it wiggled off the terminal of the cabinet.

[@mark.r8900]

Great video as always. I was checking the flame sensor signal on a mid efficiency furnace. When furnace fires up the microamp was around 1.7uA. But within a couple minutes the reading started to drop from 1.7uA to 0.6uA and furnace shuts off. I've checked all grounding, changed flame rod, verified gas pressure, cleaned burners, checked all connections and wires, checked rod distance from burner. The board is sending around 110vac to rod. Can it be a bad board? Thank

[@light0000]

I'm struggling with my HSI not glowing. I replaced it and everything seems to check out. But still no glow. Did you ever figure out what your problem was?

[@light0000]

Is there any reason a bad flame sensor would not allow the HSI to cut on and glow? (Error code HSI, replaced with new one. Still doesnt glow. Code still says igniter problem)

[@jaymz0074]

Good stuff

[@farashvac]

Hello sir, how can you fix the UA reading that fluctuates on meter , has happened to newer ruud furnaces, running ground wire to burner boxe doesn’t seem to help, any ideas .?

[@jasonalmeida7096]

Is it a Lennox?

[@farashvac]

No, rheem/ruud.

[@light0000]

Help! HSI replaced along with the thermostat. Furnace still shows error code ignitor. And the HSI will not glow)

[@tonyarchuleta6529]

Just a quick question when the flame sensor is properly positioned in the burner flame is the 60 volts eliminated from that flame rod and now is reduced down to microamps 2.5 give or take a microwamp

[@caru3257]

Voltage is always present at the flame unless is not energized. Amperes are the result of voltage divided resistance. Example: 120V/60R=2A.

[@Overseaspakwan]

Good morning how are you sir can ur help me I need a freezer electric conaction with salonite vale how fixed plz update.....

[@davidhazas7162]

If a flame rod can get the micro amps reading back to the board then why do u need a separate ground wire to do that same job? This is what I never fully understood.

[@caru3257]

The flame rod is completing the path and it is going to ground after jumping the gap if I’m not mistaken.

[@prodigydude]

@@caru3257 they're basically asking why you can't have two seperate currents on the same wire

[@victormartiny6419]

Thanks

[@oso1165]

How do you check flame current on those furnaces where the voltage is fluctuating the flame rod. The micro amps will usually fluctuate from 0 to 6ua back and forth. Usually higher end Lennox and Rheem

[@bill944]

I came across an SLP98 the other day that had a week flame sense error. Milliampers was jumping all over from 0 to 12. It stayed running for me but I feel uneasy about it.

[@oso1165]

@@bill944 they're designed to be like that. Some of the Rheem and Goodman do as well

[@oso1165]

@@blankman8021 yes, literally what I just said...

[@Hannah-ql4ss]

My flame rod has a piece of the ceramic actually in the path of the flame so I was thinking it was replaced with the wrong style although the furnace is running fine .Any thoughts ?

[@Sceloporus9832]

Flame rod grounds on 25yo propane furnace 💪

[@AmericanFarmerHVAC2024]

How did you get those carrier burners to mount on your test bench piece? lol, very curious. Also a carrier ignitor you had too. * Nevermind, this must have been the series before the infamous carrier 58s/bryant 350s.

[@villegasluis7553]

Nice vidio

[@yulandasoscia2211]

HEY, Craig, another fantastic tutorial vid! We sent you a collaboration request just now. Could you tell us what you think? We are TopTes brand producing gas leak detectors.

[@MEP.ENGINEERING.WORKS92]

👍

[@makoado6010]

wow open burner like this prohibited to sell in eu cc 15years ago.

[@jessestewart3835]

The combustion chamber door has been removed....

[@rcstl8815]

There are units older than that still in service. My 1993 yorky90%er has a sealed burner box but I have seen other newer units with open boxes. Newer would be later than 1993, haha. Next August it will be 30YO. It is in a dry, low humidity location and the safeties have always been in place and working. Regular low restriction filter changes. So the exchanger is still solid.

[@rcstl8815]

@Angry Beaver Keep Mongo away!

[@hornitorrincoperezoso2189]

Dude sounds like George Lucas.

[@stephwaylonwells3218]

👍