Gas Furnace Flame Rod Sensor and Rectification Explained!
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- Опубліковано 8 вер 2024
- In this HVAC Video, I go over the Flame Rectification Process and how it is used to detect if there is a Flame. I explain how to do a normal test to check for DC Micro Amps. I go over where the flame rod is placed compared to the ignition source, how the voltage travels through the flame as well as other tips! Supervision is needed by a licensed HVAC Tech before doing this as Experience and Apprenticeship garners Wisdom and Safety.
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I still need some help. I understand the flame sensor sends say 90 volts to the metal probe, from there the voltage travels through the flames ions turning into direct current flowing upstream from the flame to the burner face....but then what happens next, I don't understand stand?
Finally...A no nonsense "full explanation" or the flame sensing process....I have been experiencing an intermittent problem with burner drop out....Now I know the burner surface needs cleaned as well as the flame rod and the importance of a good grd....Thank you for this video.
Thanks a lot Vern!
My respect and gratitude for sharing what you know. You are helping a lot of technicians who want to learn get better. Who ever gives a thumb down in my opinion has stopped learning but you are one of the best teachers I’ve seen on line.
Thank you !!
Thank you very much Felix!
This is gold! I've always been cleaning only the rod and never the burner retention head. I've been having problems with a goodman gmvm97 flame sense. I've been getting called back every month. Next time I'll be cleaning the burner and also checking voltage between neutral and ground.
lad to help Jshortca!
Amazing information for a DIY person, I was thinking that it was transferring the heat to the board, but I see your amazing explanation and understand now how it works. I'll have my multimeter readings to see the issue of my furnace is cutting the fire after 10 seconds. Thanks.
Fantastic video! Thank you for the thorough explanation!
First time I did listening to the explanation got to repeat it three times till understand. That "through the flame" drove me nuts :D
Flame rectification is a little harder to comprehend, thanks Juan!
Man I wish I would’ve seen this video a few days ago. 😂 recently I did a PM on an older Rheem furnace, that wasn’t sensing the flame after I cleaned the flame rod. It generated no DC micro amps, so I assumed I broke it somehow. I put a new one in there and it did the same exact thing, thinking maybe the new rod was defective somehow. So I put a different new rod in there and still did the same thing. I went crazy trying to figure out what the issue was. Had continuity from the flame rod all the way to the board. I began to assume the board was bad, called the boss to verify, and to just replace it with one of our universal boards. Anyways, had I known how the flame rod works NOW, would’ve saved me so much headache. My theory now is that the board was likely not sending 115v to the rod.
But the stress and headache didn’t end there! When I put the universal board in there (according to the manual for the new board, it was compatible with this Rheem), as soon as I gave it power, immediately it flashed the trouble codes for “unexpected flame sense” and “pressure switch stuck closed,” neither of which were occurring. I assumed the new board was defective, called the boss to explain the situation. Luckily he was just down the street. Told me he had the same exact board, and to come get it and try that one instead. Put the second universal board in there and it did the same exact thing. Turns out the stupid board wasn’t compatible despite it supposedly being so. We ended up having to order the factory OEM board and put it in the next day, worked like a champ after that. I’m always learning something new. 🤣🤣🤣
This is in reference to Jesse's question on flame rectification sent through the messenger. It is not allowing me to reply so I am posting my answer here.
The question:
I just have a question on your flame rectification. I get the flame sends voltage to the burners which converts to DC. I get hooking up the meter leads in series reads the DC current moving from the flame to the burners. But how does the board confirm this to keep the flame going? People say it has to be grounded. But not all burners have a ground wire on the burner box. You can remove it and it will still run.
The boards that you disconnect that have the ground wire going to the burner may also have another ground somewhere such as the ones that go to the gas valve common and then to another ground before making it back to the burner. If it goes to ground, it could pick up the micro amp signal. You can also do that test for micro amps in series on the ground wire and to be honest, that gives a better reading for how many micro amps you are getting back to the board.
It reads the ac imput back on its self if I understand correctly. The board is looking at the flames directly through interference paterns in the flame.
thanks for the discussion.
Good video thanks. I’ve been installing for years and did not know this 😄
Thanks rijivit!
Thanks for that. No one could tell me how it worked. Now I understand. Thanks again.
Great concise explanation. Thank you.
Glad you enjoyed it!
Thanks for the video! It is really nice to know how something works as well as how to make repairs. AGain, thanks.
Thanks Joseph!
Excellent video. You really know what you do
Thanks Dan!
Great video, I knew a lot about this already but I learned even more! Thanks.
Heck of a flame rollout evidence in that burner box yo u used as example
That was awesome information.
Thanks Steve!
very nice explanation! great video.
Thanks NICK-O!
It's not the size of the chassis that causes flame rod rectification. It is the temperature difference. Electrons can leave a hot glowing flame rod a lot easier than a cold piece of sheet metal. That makes the rectification one direction. Vacuum tubes used this exact same principle with the heater element.
ohh and I'm still waiting for the pm video and more schematics videos....and yes I know you are busy with work and classes I'm just bugging you...👍👍👍
OK no problem.
nice video like always and good explanation too.
I appreciate it!
hell of an explanation thanks
Thank you for your Comment gonz garr!
Great explanation!!
Thanks Paul!
very educative thank you
Thanks Sesha!
Awesome video. Question tho.. Can the quality of the flame affect the DC voltage? If the voltage literally travels thru the flame what happens if the furnace is running rich or lean will that change the voltage??
Yes, slightly as it travels through the carbon in the flame but the board would not be able to read the difference, thanks
Great video
Thanks Paul!
Great video!😎
Thank you!
I shure will. Thanks
Glad to help! Ha, I actually just got back in from a no heat service call!
good video. What would your microamps be reading if the sensor was beginning to get corroded but still proving a flame?
Thank you!
does a flame sensor have to turn red to work properly?
thanks nice video.
I have a question about the Ground. Can you explain how a bad ground can cause intermittent voltage, causing loss in voltage at the gas valve.
I will have another video coming out on the flame rectification process. This one will be for testing. Problems arise from ground to the board, potential voltage measured on the ground, and flame position as well as oxidation on the rod. Thanks!
I've heard Teflon tape can not be used on gas pipe because it can interfere with flame rectification. Is that true or does the system rely on electrical system grounding independent of gas pipe threaded connections.
Flame rectification usually travels through the pilot tube for pilot ignition and direct ignition usually travels through the burner retention head and ground chassis but yeah I don't use the teflon tape rated for fuel gas but just thread sealant. You don't want an inspector to fail you and you do want your piping to have continuity as well for ground, thanks Joe!
What would be the reason that, there won't be any microamps when tested? Could it be ground or electronic board problems?
Check for voltage going to the flame rod. One probe on the 120v common and the other on the hot feeding the flame sensor. It should be 90-110v. Is the flame rod in a good place enveloped by the flame? If so, you should be reading at least some micro amps if you are in series on dc microamps. Thanks and let me know how you make out.
Goodmorning sir, question;
In order to confirm the boards operation, prior to flame rectification, will testing the Flame Sensing terminal to ground provide AC voltage reading? If so, would that be a proper indicator that the board is performing its sequence?
It will provide an ac voltage reading but only shows one facet of the board checking its safeties, thanks!
hi, on a york rtu the flame sensor sits in front of the pilot tube rail instead of the main burner. so how does this work? the main burner flame is not touching the rod at all. does this mean the pilot is on all the time and the rod is only sensing the pilot flame? the unit has an intermitten ignition control board. thank you.
Ha ha, yes, crazy huh? The rectification is only checking the pilot and not the main burners. That is how the older furnaces used to work.
i didn't understand well what you mean about flame rod have to be one-fifth of the head. could you explain more? You are speaking about lenght of the rod comparing with ???
I was speaking about surface area. For instance if you compare it to the flame rod on a smart valve which is much smaller, thanks!
For the life of me I cannot get any DC uA readings on the ground side of my Rheem RGPH-07EAUER; it doesn't even fluctuate, it's always 0, yet the readings are great on the source side. Checked ground connections multiple times with 0 ohms, and 0vac from ground to neutral. 0 ohms from the flame sensor signal wire back to the IFC. I'm beginning to think my model doesn't use the ground side to send the signal to the IFC, b/c occasionally the burners will stay lit and the unit will work for a couple of days, while the readings on the ground side are still 0. Most of the time, the burners will not stay lit for more than 8 - 25 seconds. I've replaced the flame sensor and even the IFC board, and also cleaned and sanded the burners and the whole area around them. This thing is possessed! I replaced the gas valve, unit worked for two days. Removed the ground wire from gas valve, unit worked for 3 days. Removed the red wire connected to the IFC board labeled fan, the unit ran great for 5 days. I don't understand how doing any of these random things get the unit back into a temporary working order, and most of all, why the hell are they only temporarily!
Did you change your filters?
Did you figure it out ?
So there's two wires on the flame sensor
250,000 Craig go for you
There are many other videos showing how to clean the Flame Sensor. Many of those videos state how you shouldn't be touching the flame rod because of the "oils on your skin" - is this just a myth? Surely the flame would burn off anything like this that is a bad conductor. They also mention not using anything "too coarse" to clean the rod. How could scratching a stainless steel rod ever reduce its ability to conduct electricity?
The skin and oil touching is actually the hot surface ignitor. I think that migrated over from the hsi to the flame rod just from people telling other people. If you scratch the rod then it is not as smooth and insulation sticks on it and could impede the voltage flow so yes use a non course unsoaped steel wool. Really it is more less just common sense. Nothing to stress about if you touch the rod, it is just stainless steel. On the flip side, always take extra precaution to not put anything in the way of the system working properly. Because of the questions you have asked, I can tell that you have a grip on the topic! Thanks for the questions!
@@acservicetechchannel Excellent answer to a common question and myth, thanks !!
Sorry. I sure will
I do mean I am glad to help. I just thought it was funny walking into the house and going to the computer to check on everyone, that's all.
I was told to don't touch the rod, now what???
Whoever told you that was speaking about hot surface ignitors. A flame rod is literally just a stainless steel rod that voltage travels through. You won't hurt that but you could clean it with unsoaped steel wool before reinstalling it, thanks!
very confusing,doubt anyone got that; maybe a simple hand drawing on paper
I changed the flame rod, and there was no change
Most times it is a corrosion problem on the rod but you already changed that out or a ground problem but even if you had a ground problem, you would likely still be reading micro amps dc on the supply voltage side when in series. Let me know how you make out. Thanks
hello. i am struggling with a Rheem furnace from 1990 furnace serial AG5D304 F3090 6468 and MODEL RGLE-06NLAER which does not have a flame sensor and instead the igniter acts as the flame sensor from what i understand. the gas valve keeps shutting off at various times without any good reason. it is not immediately after ignition. it can run for hours or minutes before shutting down.The limit switches don't seem to be the problem (i checked for opens) and the gas valve only shuts off when it doesn't get 24 V. the thermostat controls the inducer motor perfectly so i don't think it is the thermostat. how do i know if the problem is the sensor portion of the igniter ( since ignition function works perfectly), or the main control board or the ignition module? i think the gas valve signal comes from the ignition module in this model but i am not sure. I would like to verify before buying these parts. any help would be much appreciated.
Check out this ignition playlist especially then the single rod honeywell one (Gas Furnace Spark Ignition Control Troubleshooting! ) Many times it is the flame rod or pressure switches. The pressure switch may be fine but omething may be tripping the pressure switch. Is there an error code from a flashing light? - ua-cam.com/play/PLxnHR5_D2ojwefn5vubZ7A8MA89Z6AnMU.html
thx, no it's old board with no code LEDs. i can try to catch when it acts up and see if the pressure switch is open. am i just measuring 24v at both leads of the switch? then i will know if it is the pressure switch that remains open, right? i will also try to get to the leads on the ignition control module. By the way, this is a hot surface igniter not a spark one. do they all work the same? in terms of retrification? a couple of other questions, i measure two thermal switches when it fails and they aren't open ( 24 v on both leads). somehow, when i close the doors in the front, it shuts down more quickly it seems. as if there is another thermal switch measuring the ambient temp in the furnace? what else would closing the doors do to make it shut down quicker? (no door switch involved)? sorry for the length of comment. i would like to send you a picture of circuit diagram. is there an email address i can reach you at? thx for the great help !
When you said you thought the ignitor was also the flame sensor, I assumed it was a single rod setup. You want to power the furnace without a call for heat and see what side of the switch normally has the 24v. If that doesn't work, turn the power off, unplug the inducer, turn the power back on and turn the tstat to heat and turn temp up. You will have 24v on one side and not on the other since the inducer motor is not running. Any way once you figure this out, you will know which side of the pressure switch to check. It will be the other side. Put one lead on the spade term on the pressure switch and the other on the c terminal or ground to pick up the 24v going through the pressure switch. You should also T in a pressure testing digital manometer so that you can see any variation in the negative pressure while running. You can send emails to info@acservicetech.com If this happens sooner with the door shut maybe the furnace is having a problem exhausting or maybe the thermal heat switch is going on the heat exchanger air area. I was able to pull up the first 4 characters of that model number and it looks like it is an 80% eff furnace so you mwouldn't have to worry about a condensate drain pressure switch line. When I looked it up though it says Direct spark ignitor and not a hsi. If it is a flame and ignition rod, it needs to be cleaned with unsoaped steel wool. Thanks- check out the furnace troubleshooting playlist for any other videos and testing of components- ua-cam.com/play/PLxnHR5_D2ojyN6VClLntbM4X82Gc9Xs8A.html
hi there. i sent you an email with the attached diagram. thanks so much.
hi i sent you an email with attached diagram. thank you very much.
STOP SAYING "SO" & "HERE"!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
good video. What would your microamps be reading if the sensor was beginning to get corroded but still proving a flame?
It may be lower like 2 microamps or less. The microamp measurement could also be intermittent.