Without an understanding of what a diode is no one would understand how this works. The flame sensor acts as the anode and the blue part of the flame is the cathode. A sinewave signal is sent to the flame sensor terminal from the spark module and rectified (half wave) since it acts as a single diode rectifier . The spark module picks up the signal on the burner side and inputs it into a detection circuit to detect flame presence.
I agree. I love you, Ty, but he actually correct. Granted, a lot of people will (hopefully) grasp the basic concept of flame rectification after watching this video. But if we wanted to get technical (as you know some of us do! 😆), we would need to teach the principle of how diodes and electrochemical reactions work. Some are actually going to think that the flame generates the signal needed to prove itself. (There were a few classmates of mine who actually thought this was occurring.) "If we place a light bulb inside the flame, would it turn on?" 🤦🏻♂️ Also, Ty, when you were demonstrating how to check the microamps with your multimeter, you had the camera pointed below the display of the multimeter; we couldn't see how many microamps were being measured by the meter. 🤦🏻♂️
A most excellent Flame Rectification video. Next is to hookup an oscilloscope to the wire and check out the pulsating DC voltage waveform. Just to see what it looks like? 😎 Thank you.
Yes it does work most of the time. If someone cleaned it with sand previously, or there are a lot of contaminants in the air it's sometimes not enough. Have you seen the new white Rodgers Emerson universal flame rods?
Just paid $850 for a technician to replace my gas valve only to find it was the flame sensor. They still haven't diagnosed it and are trying to convince me the unit has multiple issues and needs replacing. Had to go up and do it myself by cleaning the flame sensor. Working fine now. Wish I had known this earlier!
I'm glad I could help. There are 2 problems here: #1 Unfortunately the skilled trade shortage has caused a lot of people to enter the trade without the training, knowledge or skills needed. #2 Private Equity companies are buying HVAC companies and pushing sales sales sales. They spend a ton of time on sales training because new units have the greatest return. Technical training costs more and has the least return for the company.
I was wondering how a flame sensor worked. I always assumed they were like a thermal couple and was curious as to why they wouldn't work when they got a little dirty. I had no idea it was reading continuity through the flame. Thanks for the clarification.
Thanks for the information I went to my moms house today because she said she had no heat I cleaned the the flame sensor and bam all is good now. The unit is 5 years old and probably should of had some maintenance beside filter swaps
Awesome video! Best explanation I’ve seen! Quick question. It is my understanding that the flame sensor receives 120volts from the board. Can we also test for voltage to the flame rod ? Also if the flame is doing the rectification, how does it read the micro dc amps before the flame? Thank you in advance sir.
Boards don't always have the rod energized and they are not always 120v. Once the voltage is converted to a pulsating DC, it travels on the ground or casing of the unit. The board is also founded and it reads that unique signal. Some boards read micro amps to the flame sensor. The small amperage is how it knows.
Great video but...what about earlier, older model gas furnaces (Bryant, Day & Night, Payne) that do NOT use a flame sensor rod. How does the so called "Safety Pilot"(flame sensor) work, how to test, can it be cleaned???
Really great explanation of flame rectification. I have a fireplace that has a spark fired pilot. I’ve can see that I’m not getting a spark, so is there a way for me to prove that it’s the control board or the actual wire and rod is the problem. I’d like to be able to check the current or.voltage to see where the problem actually exists, like how you check the uamps coming of the flame rod. Thanks for any assist.
It's usually a dirty ignitor rod or the board, rarely the wire. You can get a spark tester from an auto store, and test it from the board to ground if you want to know for sure.
Left unanswered: what level of current is acceptable? Apparently the current decreases as the probe gets dirty, so at what point will the computer shut off the gas? 4 microamps? 1? Who knows? Maybe it's 5.2 and this unit will fail next week.
It varies by the manufacturer. Anywhere from . 5 to 10. Anytime your there, properly clean the flame sensor. Even if the call was unrelated clean the flame sensor.
Very cool presentation. Too bad I watched it AFTER I used 400 grit on my flame sensor. Oh well, it works fine, but I'll keep on eye on it. Worst case I'll have order a new sensor in if it acts up. I was pretty gentle with it and used alcohol to clean it up after. Hopefully that removed the silica.
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 you.
Ran into a issue with flame rectification. I’m getting no uA on three different sensors one of which came from a neighbor with identical unit that works. I’m getting continuity across all bonds and grounds. I pulled burners and brushed them clean. My question is can the board prevent you from getting a uA reading? I got 25v from sensor to wire. What am I missing ?
Proper polarity to the unit is important as well as a proper receptical plug ground. Then make sure the wire from the board to the flame sensor is good. Is all that is good inspect the board for water spots or burn spots. May be the board.
My flame sensor is mounted near the electronic controlled pilot light. When the pilot light lights, the meter reads 1.5uA. When the gas valve fully opens it jumps to 4.5uA. After running for a few minutes, the current jumps to 6.5uA. Does this sound like a dirty/bad flame sensor? (I bypassed the control board to get the pilot light/gas valve to turn on for this test as the system keeps shutting down.)
That sounds like a smart valve. They are not meant to be cleaned, the mini hsi breaks very easily as does the flame sensor itself. Notorious the plug connector at the valve becomes loose. It is normal to get higher UA when the main burners fires.
The pulsating DC current there the ground is the "signal" going back to the board. We can read UA but most boards look for the pulsating DC at the ground from the flame rectification.
Hi, I have a flame sensor signal of about 0.6uA. The furnace shuts off after 5 seconds. I replaced the flame sensor but same results. Can a bad furnace control board cause this problem? All grounds and wires seems ok.
@@mark.r8900have you found the root cause? I have a similar issue. I do not have a multimeter that is capable to the current in the micro-ampere range, but the furnace shut off a few seconds after it fires up. I measured the AC voltage across the flame rod and the furnace ground, it read about 2 Volts AC. I believe the voltage is supposed to be in a range of ~40 to 120V. This voltage is applied by the control board. I suspected the control board could be bad.
My furnace has a smart valve and it keeps turning off after 5 seconds I change the flame sensor and still doin the same do u think is the control board or the smart gas valve problem ?
the plug where the igniter fits into the valve body. Its a known point of failure, some people have been known to force an object in the back side of the plug so it keeps pressure forced against it.
It’s crazy to me you can use your meter leads attached to the meter to complete the circuit and heat comes on, but we can’t use our meter leads attached to the meter to jump out the stat and give a call for heat or cooling. I’m missing something here idk how that’s possible. Also I believe the flame sensor terminal on the control board still has voltage even with the wire removed.. any help is greatly appreciated!
Contrary to popular belief, it does not have a coating. However if you use sand paper, the sand leaves a residue that cooks into a silica coating that increases resistance and causes issues over time.
It doesn't, AC is supplied to the rod but it can't go anywhere. When the flame ignores it created a path for electrons to flow but due to the ions it can only flow in one direction. So the electricity is flowing threw the flame in a pulsating DC way. The CO trip board reads this to know there is a flame.
Voltage can be 20-120 to the flame rod depending on manufacture. As techs we can measure the microamps but the board is reading the pulsing DC signal caused by the flame carrying and rectifying the circuit. This is why the burners and the board must be properly grounded. It's also why a rusted burner face can cause a poor flame signal
@@love2hvac Understood. I have an old house in Oakland that I lived in for 40 years and the furnace dates to the late 60's (found a date code when I was troubleshooting 7 or 8 years ago.) That time it was a tired thermo couple. The house has been rented out for the last 4 years and a couple of weeks ago the tenants called and said the heater quit working. I sent them a you tube vid about relighting the pilot and was able to talk them through getting it relit and working again. For years I'd do the filter c/o and putting a few drops of light machine oil in the 4 oil cups. It's been a good unit, but there is a part of me that would like to go through it a bit more thoroughly with someone who does this on a regular basis.
I use 2000 Grit Ceramic Sandpaper to clean the ignitors and then wipe them clean with rubbing alcohol. Would this fine grit leave ceramic residue on the ignitors even after wiping them with alcohol???...any input is appreciated!
