Here's a good explanation of how the flame rod works.
Now that I know how it works, I should be able to devise
a test that doesn't require me to measure 5 ua of current.
trader_4 wrote, on Tue, 23 Dec 2014 06:56:45 -0800:
You're definitely on to something here!
This video says reversed polarity will cause teh flame sense to not work!
Look at the test here for ground using AC voltage (< 2VAC):
From this video, the FS terminal (Flame Sensor) on the board is key:
That control board FS terminal sends out a signal of 90VAC to the flame rod.
The flame itself, acts like a diode and a resistor, connecting the flame rod
to ground, which is the burner metal itself. Completing the circuit causes
the control board to hold open a relay, which keeps the gas flowing.
I noticed my burners were rusty on their ends, so, I will try to clean
Any ideas how to clean up this burner end?
On Wednesday, December 24, 2014 10:03:05 AM UTC-5, Stormin Mormon wrote:
I agree, if there is loose rust. From the pic I saw, it just looked
like one end was rusty. If it;s just a light rust coating that isn't
loose, I'd just leave it be. If you take it to bare metal, it's just
going to repeat the rusting process.
They may have told you that, but I've never had a
problem buying from them, and I'm not a contractor.
It's close, just drive over. Then stop at the
falafel drive-in across the street for a gyro & baklava.
The COM terminal is used in conjunction with the RED terminal to
provide power to 'smart' thermostats like the Nest or the Honeywell
units that have Wifi radios and other circuitry that needs constant
trader_4 wrote, on Wed, 24 Dec 2014 04:13:39 -0800:
I have to agree with you.
One of the videos I watched was from a teacher who sabotages furnaces
as a test for the students, & he said he can't make a flame sensor fail.
It's simply a stainless steel rod, mounted in an insulator, which is
just about the simplest and most rugged of all possible sensors.
a. The rod can get carbonized (hence less conductive)
b. The insulator could lose its insulating abilities (not likely)
c. The burner can lose ground (or develop high resistance).
Even though I have a new flame sensor on order, I can't imagine that
there is anything wrong with my current flame sensor, since, as you note,
the thing is just a steel rod.
trader_4 wrote, on Wed, 24 Dec 2014 04:04:51 -0800:
In my case, everything is working, so I guess that the "component test"
didn't tell me anything.
The only problem is that the flame is incorrectly *not* being sensed,
but the "component test" doesn't seem to turn on the flame, so, it
wouldn't know that.
trader_4 wrote, on Wed, 24 Dec 2014 04:20:58 -0800:
Since the flame lasts about 7 seconds, there was time just now to
test the shutoff by shorting the flame sensor to ground within that
seven second window. But, as you guessed, nothing different happened.
Tony Hwang wrote, on Wed, 24 Dec 2014 08:45:40 -0700:
I think I have three choices right now:
1. Bad flame sensor
2. Bad control board
3. Bad ground for the control board or flame sensor
I think the flame sensor being bad is really remote, only
because the thing is simply a rod, and I've cleaned it with
emery cloth to no avail.
The control board may be bad, but, it's certainly giving the
flame sensor the nominal 90VAC that it's supposed to give it.
Here you see a reading of 104VAC from the flame sensor input
wire to ground, which can only be coming from the control board.
Yet, when the flame sensor should be outputting 1ua to 6ua, it
actually outputs nothing, even when tested with a sensitive meter:
I even grounded the burner with a jumper and nothing changed.
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