On Tuesday, December 23, 2014 11:36:56 PM UTC-5, Danny D. wrote:
Tony Hwang wrote, on Tue, 23 Dec 2014 13:57:56 -0700:

Just with a short piece of wire jumper the TP and ground
momentarily the test will start.

I don't understand that test.

It "sounds" like a good idea, and it's *easy* to run:
https://c4.staticflickr.com/8/7559/1...ed919914_b.jpg

But, whatever it does, doesn't tell me anything.
It just runs 'stuff', and that's about it.

I must be missing the magic of this so-called "component test".
I *wish* it gave me useful information.

But, I get nothing out of it, and, I'm not even sure that the
"component test" tests the flame sensor anyway, since the flames
never start up during that so-called "component test".

So, at the moment, I think it's the most over-rated test that
has been suggested, to date!

It's not over-rated if the inducer blower, air handler blower, etc
has failed.....

On Tuesday, December 23, 2014 11:49:39 PM UTC-5, Danny D. wrote:
Scott Lurndal wrote, on Tue, 23 Dec 2014 21:28:09 +0000:

http://www.bitscope.com/product/BS05/

Thanks Scott,

I have a call to a scientist friend, who might have the capability
to measure 1 to 5 microamperes of current.

A funny thing is that one of the service personnel told me to
measure "5 ohms" (I swear I heard him right) of the flame sensor.

When I questioned him, he said he always measured if it was 5 ohms.
When I asked him *how* he measured it, he *clearly* explained that
he hooked one lead to the disconnected wire and the other lead to
the spade on the flame sensor while the flames were heating it up.

He kept telling me that was ohms, and I told him two or three times
that he can't possibly be measuring ohms that way, but he insisted
he tested the ohms that way all the time, and determined whether a
flame sensor was bad that way.

Sometimes these technicians scare me.

Maybe he's not as dumb as he sounds. If you put a VOM on the ohms
setting, it's providing a voltage source. You now have that connected
to the flame sensor. The flame sensor apparently only conducts in
one direction, but if you had the polarity right, you would think it
would pass some current through the flame, just like under normal
operation. That in turn would result in the VOM reading some kind
of resistance. But you'd think it would be a lot higher than 5 ohms.
And that also assumes he meant you should test it installed, with flame.

Now that we all know how the flame sensor works, I'm left wondering
what there is to fail? It's just an electrode. About the only thing
that I can see that could fail would be either the attachement wire
coming loose or the insulator failing. Both of those should be testable
with a VOM, without the need for flame, etc. But maybe something can
change in the surface of the metal that reduces it's ability to conduct
too.

On Wednesday, December 24, 2014 12:23:26 AM UTC-5, Danny D. wrote:
Scott Lurndal wrote, on Tue, 23 Dec 2014 21:28:09 +0000:

http://www.bitscope.com/product/BS05/

I got an idea for a test of the "flame rod" from this video.
https://www.youtube.com/watch?featur...06j2CE#t=15 8

The guy shorts out a good flame rod, and the flames stop.

If I short out mine, during the flames, it should also stop the flames
quicker, and, if it doens't stop the flames right away, that would be
an indication that it's not doing anything.


I didn't watch the video, but I'm guessing that he did that with
a furnace that started up and was operating, ie it was past the first
few seconds. From what you've said, yours isn't doing that. The
sequence is the furnace turns on the gas, ignites. At that point I
would think it doesn't care what's going on with the flame sensor.
It's only some seconds later, when there should be flame, that I would
think the flame sensor would matter. So, past that point, if you
shorted it out, then I'd expect it would force a shutdown. But you
aren't there, you're in that initial fire up window.



Of course, either way, I still wouldn't know if the control board is
bad, but, it's worth a test to see what happens.

Also, I noticed his autopsy of a flame rod shows that there is apparently
*no connection* from the flame rod to the steel body of the flame rod.
https://www.youtube.com/watch?featur...06j2CE#t=18 6

So, it *is* a single-wire sensor!

Of course there's no connection from the rod to the metal body. It
relies on the flame to make the connection. That's how it works.

On Wednesday, December 24, 2014 3:21:37 AM UTC-5, Danny D. wrote:
trader_4 wrote, on Tue, 23 Dec 2014 06:56:45 -0800:

If the ground is affecting the flame sensor, then it't the ground path
from the metal cabinet/frame of the furnace to the control board. That's
where I'd be looking. There must be a ground wire that goes from the control
board to the frame and the frame is also grounded to the incoming AC.

You're definitely on to something here!

This video says reversed polarity will cause teh flame sense to not work!
https://www.youtube.com/watch?featur...WNRqMM#t=31 6

Look at the test here for ground using AC voltage ( 2VAC):
https://www.youtube.com/watch?featur...ApSN7E#t=49 8

From this video, the FS terminal (Flame Sensor) on the board is key:
https://www.youtube.com/watch?v=JE3MzApSN7E

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
them up. https://c4.staticflickr.com/8/7554/1...49404dd7_c.jpg

Any ideas how to clean up this burner end?

I wouldn't bother. It's just going to get rusted again. The existing
rust probably serves as a protective barrier. Remove it and you just
expose more fresh metal to oxidize.

On Wednesday, December 24, 2014 6:58:04 AM UTC-5, trader_4 wrote:
On Tuesday, December 23, 2014 7:19:34 PM UTC-5, wrote:
Ok, im a little wrong.
The flame senor works by rectification. The controller applies a small AC voltage and the flame lets the current flow in one direction only in effect creating a small DC current. The battery analogy is not exactly right..
Goggle flame rectification sensor.

Mark

Well, you learn something new all the time. I thought the flame sensor
was a thermocouple. But from some googling, I see you're right. I never
even knew this phenomenon existed. It apparently works by using the
flame itself to conduct a small current. And somehow the AC gets half-waved
rectified in the process.

One big difference with testing, would appear to be that the rod type
sensor won't generate any voltage from just heating it. It has to have
an AC current applied, so the current test would have to be done with
it installed, connected to the controller.

Now the advice to clean them makes sense. If it was a thermocouple,
whether it had some dirt on it or not should not affect the operation.

Hi trader.
yes I just learned this too, and it is interesting.
Apparently the flame sensor circuits have evolved to this. I read that the original flame sensors were just measuring the DC resistance through the flame, no flame is an open circuit, and a flame completes the circuit but with a high resistnace. The problem is that this is not fail safe. If the insulator that hold the flame sensor gets soot, that leakage resistance to ground can look like a flame. So if the insulator is sooty and the flame should go out, the controler would see the path through the soot and think the flame is present. This of course is very dangerous. So they improved the circuit, instead of just looking for DC resistnace, they found that a flame (unlike soot) conducts current in one direction better than the other. So the newer circuits apply an AC voltage, looks like a high impeandace and pretty high voltage like 90V AC and the circuit senses that there is more current in one direction than the other. This indicates that there is an actual flame and not just leakage from soot.

So I'm guessing now that the 90 or so volts comes from the AC line and the controller circuit can't work right if the AC hot and neutral and ground are not connected correctly.

OP, what kind of VOM do you have. Not all can read MICRO amps. You would have to put the meter in series between the flame sensor and the controller.

On 12/24/2014 12:46 AM, Danny D. wrote:
Danny D. wrote, on Wed, 24 Dec 2014 05:44:44 +0000:

Here, they use a $10 cheap (#69096 Harbor Freight) meter!
https://www.youtube.com/watch?featur...4OJBc4#t=20 1

As much as I hate cheap tools, I might pick one of these up:

http://manuals.harborfreight.com/man...9999/69096.pdf
Harbor Freight 69096, Cen-Tech 7 FUNCTION DIGITAL MULTIMETER


Often free with coupon and any purchase. I have
several, and find them to be very useful.

-
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On 12/24/2014 3:21 AM, Danny D. wrote:

I noticed my burners were rusty on their ends, so, I will try to clean
them up. https://c4.staticflickr.com/8/7554/1...49404dd7_c.jpg

Any ideas how to clean up this burner end?


Wire brush, and blow the loose rust out. I've had
case or two where rusty burner didn't light properly.

That could be your big problem.

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Wednesday, December 24, 2014 10:03:05 AM UTC-5, Stormin Mormon wrote:
On 12/24/2014 3:21 AM, Danny D. wrote:

I noticed my burners were rusty on their ends, so, I will try to clean
them up. https://c4.staticflickr.com/8/7554/1...49404dd7_c.jpg

Any ideas how to clean up this burner end?


Wire brush, and blow the loose rust out. I've had
case or two where rusty burner didn't light properly.

That could be your big problem.

--


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.

On 12/24/2014 10:18 AM, trader_4 wrote:
On Wednesday, December 24, 2014 10:03:05 AM UTC-5, Stormin Mormon wrote:
On 12/24/2014 3:21 AM, Danny D. wrote:

I noticed my burners were rusty on their ends, so, I will try to clean
them up. https://c4.staticflickr.com/8/7554/1...49404dd7_c.jpg

Any ideas how to clean up this burner end?


Wire brush, and blow the loose rust out. I've had
case or two where rusty burner didn't light properly.

That could be your big problem.

--


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.

The one I was remembering, there was enough
rust that the flame didn't spread from one
burner to the next. That might help explain
the lockout, here.

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

Danny D. wrote:
Tony Hwang wrote, on Tue, 23 Dec 2014 13:57:56 -0700:

I know same is the case with HSI(hot surface ignitor) Never touch HSI
with bare hand, finger oil will shorten it's life, also it is quite
brittle. And cover plate removed, don't forget to cheat the interlock
switch.

I taped over the door switch, so that's not a problem.

Thanks for the warning on the brittle igniter.

Here, where I've removed the three burner tubes, you can see that
the speckly igniter is only at the top burner, while the rod-shaped
flame sensor is only on the bottom burner, with the middle burner
being left alone:
https://c4.staticflickr.com/8/7467/1...609d3825_c.jpg

Hi,
Don't worry about the voltage out of transformer. It does not have tight
specs. Can be as high as 32V AC. IIRC, the test runs the logic sequence
up to the point of running normally. If some thing is not right
it'll tell via error code. Did you see the HSI glowing to ignite?
If so definitely next step is sensing flame by sensor, if not it'll
quit and go into lock down mode but blower is still running to cool off.
Then you have to power down and up to get out of lock down mode. If it
has ground problem then clip one meter probe to furnace frame and probe
all the [point on the board Ohmming it out to see any unusual
high resistance at any point.

Danny D. wrote:
Scott Lurndal wrote, on Tue, 23 Dec 2014 21:28:09 +0000:

http://www.bitscope.com/product/BS05/

I got an idea for a test of the "flame rod" from this video.
https://www.youtube.com/watch?featur...06j2CE#t=15 8

The guy shorts out a good flame rod, and the flames stop.

If I short out mine, during the flames, it should also stop the flames
quicker, and, if it doens't stop the flames right away, that would be
an indication that it's not doing anything.

Of course, either way, I still wouldn't know if the control board is
bad, but, it's worth a test to see what happens.

Also, I noticed his autopsy of a flame rod shows that there is apparently
*no connection* from the flame rod to the steel body of the flame rod.
https://www.youtube.com/watch?featur...06j2CE#t=18 6

So, it *is* a single-wire sensor!

Hi,
If you are stuck at this point then new sensor or board, only two
choices, right? Being retired from Honeywell I can lean on guys
still working there, electricians, process control technicians, etc.
When I need parts I get help from them. On the control board there ought
to be a chip(maybe op amp) which will convert that small amount of
current to normal logic level(5V DC) to feed to ASIC(the brain of board)
telling flame is on. One time there was a TSB out regarding one high
Wattage resistor over heating causing solder joint to fail intermittent.
I used tyo reinforce the solder joints and drill holes on the board
cover near the resister for more cooling. If this resistor has poor
solder joint, it will produce all kinda funnies.

"Danny D." writes:
Stormin Mormon wrote, on Tue, 23 Dec 2014 14:48:27 -0500:

I'd mention a couple, but you need to be in the trade to buy there.

I called a few today.

APED Appliance, San Jose 408-977-0404
(sells only to contractors)

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.

scott

In article ,
Danny D. wrote:
Danny D. wrote, on Wed, 24 Dec 2014 04:45:28 +0000:

What's harder to understand is the unswitched COM terminal.


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
power.

---john.

On Wed, 24 Dec 2014 05:00:45 +0000 (UTC), "Danny D."
wrote:

Oren wrote, on Tue, 23 Dec 2014 14:46:23 -0800:

Easy to get around. I bought a "trade" restricted part from Grainger.
They asked and I told them I was from the "government". They had no
account for the agency. Instead, this was a government cash.

I remember that story, as you've said that before, I forget why, but,
probably in reference to an AC part, when I had to fix my sister's AC
unit.

If it matters, I took all three burners out, but, there was nothing I
could see to do with them once they were out, except snap a photo:
https://c4.staticflickr.com/8/7510/1...f06fc142_c.jpg

That did enable me to confirm that the flame sensor, which is on the
lower burner in the photo below, was mounted squarely in the flame:
https://c4.staticflickr.com/8/7467/1...609d3825_c.jpg

Googling for how the flame sensor works, it seems very few people
actually know, or, if they do, they are all explaining something
different.

How does a flame sensor work and how do you test it:
http://heatingandaircooling.com/2012...-flame-sensor/

How does a furnace flame sensor work:
http://www.ehow.com/how-does_4924695...nsor-work.html

How does the gas furnace flame rod work:
https://www.youtube.com/watch?v=uJU3806j2CE

etc. (I'm still reading up on this...)

I have no clue. I have read that on grills, stoves and some gas faux
fireplaces - the ceramic on an igniter can be cracked that can short
out and cause them to not work. Isn't the ceramic meant to insulate
to prevent that? Something to do with the gas valve not opening or
not staying open, thus the unit shuts down. The cracked ceramic is not
always visible. Wish I could help.

On 12/24/2014 2:26 PM, Oren wrote:
I have read that on grills, stoves and some gas faux
fireplaces - the ceramic on an igniter can be cracked that can short
out and cause them to not work. Isn't the ceramic meant to insulate
to prevent that? Something to do with the gas valve not opening or
not staying open, thus the unit shuts down. The cracked ceramic is not
always visible. Wish I could help.


Some devices like gas ovens, the igniter has to flow a
certain amperage, to allow the gas valve to open. I've
seen that once, the igniter glowed, but check with
ammeter finds it was the wrong current value. The parts
house guys saved me, I was about to replace the gas
valve.

-
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Wed, 24 Dec 2014 16:14:00 -0500, Stormin Mormon
wrote:

On 12/24/2014 2:26 PM, Oren wrote:
I have read that on grills, stoves and some gas faux
fireplaces - the ceramic on an igniter can be cracked that can short
out and cause them to not work. Isn't the ceramic meant to insulate
to prevent that? Something to do with the gas valve not opening or
not staying open, thus the unit shuts down. The cracked ceramic is not
always visible. Wish I could help.


Some devices like gas ovens, the igniter has to flow a
certain amperage, to allow the gas valve to open. I've
seen that once, the igniter glowed, but check with
ammeter finds it was the wrong current value. The parts
house guys saved me, I was about to replace the gas
valve.


I'd be curious if the ceramic on the flame sensor is cracked. Causing
it to ground out, not carry the current needed? I have no clue as an
amateur. A minor leak of power?

On 12/24/2014 5:33 PM, Oren wrote:
On Wed, 24 Dec 2014 16:14:00 -0500, Stormin Mormon
Some devices like gas ovens, the igniter has to flow a
certain amperage, to allow the gas valve to open. I've
seen that once, the igniter glowed, but check with
ammeter finds it was the wrong current value. The parts
house guys saved me, I was about to replace the gas
valve.


I'd be curious if the ceramic on the flame sensor is cracked. Causing
it to ground out, not carry the current needed? I have no clue as an
amateur. A minor leak of power?


In this case, the igniter (also called HSI)
had a small crack, and was not flowing enough
amperage to satisfy the gas valve.

-
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

trader_4 wrote, on Wed, 24 Dec 2014 04:13:39 -0800:

Now that we all know how the flame sensor works, I'm left wondering
what there is to fail? It's just an electrode. About the only thing
that I can see that could fail would be either the attachement wire
coming loose or the insulator failing. Both of those should be testable
with a VOM, without the need for flame, etc. But maybe something can
change in the surface of the metal that reduces it's ability to conduct
too.

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.

John Haskey wrote, on Wed, 24 Dec 2014 19:14:37 +0000:

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
power.

In my case, the COM seems only to be used for the outside air
conditioning unit.
https://c1.staticflickr.com/9/8669/1...03e811cb_b.jpg

trader_4 wrote, on Wed, 24 Dec 2014 04:04:51 -0800:

It's not over-rated if the inducer blower, air handler blower, etc
has failed.....

Fair enough.

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.

Tony Hwang wrote, on Wed, 24 Dec 2014 08:35:02 -0700:

Did you see the HSI glowing to ignite?

Igniter works fine.

I borrowed a more sensitive meter from a neighbor, which can read
down to 1/10 of a microamp.

It reads zero microamps when the flame is heating the flame sensor:
https://c4.staticflickr.com/8/7544/1...4bdbdf1a_b.jpg

trader_4 wrote, on Wed, 24 Dec 2014 04:20:58 -0800:

So, past that point, if you
shorted it out, then I'd expect it would force a shutdown. But you
aren't there, you're in that initial fire up window.

Fair enough.

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.

https://c4.staticflickr.com/8/7487/1...78da620b_b.jpg

Tony Hwang wrote, on Wed, 24 Dec 2014 08:45:40 -0700:

If you are stuck at this point then new sensor or board,
only two choices, right?

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.
https://c4.staticflickr.com/8/7547/1...41d3cfc5_b.jpg

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.
https://c1.staticflickr.com/9/8599/1...ec932464_b.jpg

Yet, when the flame sensor should be outputting 1ua to 6ua, it
actually outputs nothing, even when tested with a sensitive meter:
https://c1.staticflickr.com/9/8611/1...aecc44dc_b.jpg

I even grounded the burner with a jumper and nothing changed.

trader_4 wrote, on Wed, 24 Dec 2014 04:03:16 -0800:

The incoming ground will be connected to the cabinet
frame, typically right where the connection is made.

I think my next step is cutting the control board out of
its connection and looking specifically at the ground
connections to the chassis.

trader_4 wrote, on Wed, 24 Dec 2014 04:23:53 -0800:

I wouldn't bother. It's just going to get rusted again. The existing
rust probably serves as a protective barrier. Remove it and you just
expose more fresh metal to oxidize.

Too bad I had not seen this wise suggestion, as I did it already, and
it failed to improve anything.

What I did was scratch off as much rust as I could with emery cloth
and a file on the burner itself:
https://c4.staticflickr.com/8/7547/1...41d3cfc5_b.jpg

I even used Naval Jelley to remove some of the burner rust:
https://c4.staticflickr.com/8/7559/1...0d6829ef_c.jpg

But, after scraping down to metal, & re-installing ... nothing changed:
https://c1.staticflickr.com/9/8635/1...0c42c504_b.jpg

I have nominally 90VAC (actually 102VAC) on the flame sensor, but,
0.00ua of current is flowing across the flame to ground:
https://c4.staticflickr.com/8/7487/1...78da620b_b.jpg

Stormin Mormon wrote, on Wed, 24 Dec 2014 10:03:01 -0500:

Wire brush, and blow the loose rust out. I've had
case or two where rusty burner didn't light properly.

I used a file and Naval Jelly and medium emery cloth to no avail.
https://c1.staticflickr.com/9/8651/1...312e019b_b.jpg

In this picture, the right burner is the one I sanded:
https://c1.staticflickr.com/9/8635/1...0c42c504_b.jpg

It didn't make any difference, even when I added an additional
black ground jumper from the burner metal to chassis ground:
https://c1.staticflickr.com/9/8611/1...aecc44dc_b.jpg

Stormin Mormon wrote, on Wed, 24 Dec 2014 10:24:11 -0500:

The one I was remembering, there was enough
rust that the flame didn't spread from one
burner to the next. That might help explain
the lockout, here.

In this case, the flame is spreading from the top burner
(where the igniter is mounted) to the next two burners,
where the burner furthest from the igniter (which is the
bottom burner) has the flame sensor.

They designed the system that way, according to what I read,
because the burner furthest from the igniter is the burner
most likely not to light, if there is a propagation issue.

In my case, all three burners light just fine. In fact, I
am clueless how the flame moves from the top burner to the
next two burners. I guess the flame leaps down from the top
burner to the middle burner due to the unburned propane gas
initially dissipating? And then the same thing, I guess,
happens to make the flame move to the bottom burner where the
flame sensor is mounted.

In this picture below, the left flame sensor is the bottom
one that I cleaned of rust, down to the bare metal.
https://c4.staticflickr.com/8/7547/1...41d3cfc5_b.jpg

It didn't make any difference.

trader_4 wrote, on Wed, 24 Dec 2014 03:57:56 -0800:

One big difference with testing, would appear to be that the rod type
sensor won't generate any voltage from just heating it. It has to have
an AC current applied, so the current test would have to be done with
it installed, connected to the controller.

There is supposed to be 90VAC but I measured 104VAC being applied by
the control board to the flame sensor rod:
https://c1.staticflickr.com/9/8599/1...ec932464_b.jpg

makolber wrote, on Wed, 24 Dec 2014 06:03:12 -0800:

OP, what kind of VOM do you have. Not all can read MICRO amps.
You would have to put the meter in series between the flame
sensor and the controller.

I have a Fluke 75, which can only get to around 1ma:
https://c4.staticflickr.com/8/7463/1...2757e870_b.jpg

However, I borrowed an Alpha 2360, which can read to 1/10ua.
https://c4.staticflickr.com/8/7487/1...78da620b_b.jpg

When I tested the AC voltage, I put a lead on ground and another
lead on the white wire from the control board to the flame sensor.

To test the DC current, I put one lead in the white wire from the
control board & the other lead on the flame sensor spade connector.

In that picture above, you can also see that I've added a black
jumper so that I could short the flame sensor to ground, in the
middle of the 7-second flame.

All I can say is:
a. The sensing of the flame failed.
b. The flame sensor is getting its nominal 90VAC from the control board.
c. There is no current whatsoever when measured in series with the flame
sensor using a meter capable of measuring 1/10ua.

Oren wrote, on Wed, 24 Dec 2014 11:26:23 -0800:

The cracked ceramic is not always visible. Wish I could help.

The ceramic and the stainless steel rod both look pristine and
measure infinite resistance between the metal of the mount and
the metal of the rod.
https://c4.staticflickr.com/8/7523/1...f1054855_c.jpg

Stormin Mormon wrote, on Wed, 24 Dec 2014 17:49:41 -0500:

In this case, the igniter (also called HSI) had a small crack, and was
not flowing enough amperage to satisfy the gas valve.

I didn't remove the igniter, but it looks intact in my pictures:
https://c4.staticflickr.com/8/7467/1...609d3825_c.jpg

Besides, the igniter is definitely starting the first flame,
which is starting the second flame, which is starting the third
flame.

The problem is that this third flame is going out because a flame
is not being sensed. It's a false error.

There's actually nothing wrong with the furnace, except that the
flame isn't being sensed properly.

On Wednesday, December 24, 2014 11:45:30 PM UTC-5, Danny D. wrote:
trader_4 wrote, on Wed, 24 Dec 2014 04:13:39 -0800:

Now that we all know how the flame sensor works, I'm left wondering
what there is to fail? It's just an electrode. About the only thing
that I can see that could fail would be either the attachement wire
coming loose or the insulator failing. Both of those should be testable
with a VOM, without the need for flame, etc. But maybe something can
change in the surface of the metal that reduces it's ability to conduct
too.

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.

You didn't get the tank filled with non-conductive propane, instead
of the conductive kind, did you?

On Thursday, December 25, 2014 1:06:28 AM UTC-5, Danny D. wrote:
trader_4 wrote, on Wed, 24 Dec 2014 04:23:53 -0800:

I wouldn't bother. It's just going to get rusted again. The existing
rust probably serves as a protective barrier. Remove it and you just
expose more fresh metal to oxidize.

Too bad I had not seen this wise suggestion, as I did it already, and
it failed to improve anything.

What I did was scratch off as much rust as I could with emery cloth
and a file on the burner itself:
https://c4.staticflickr.com/8/7547/1...41d3cfc5_b.jpg

I even used Naval Jelley to remove some of the burner rust:
https://c4.staticflickr.com/8/7559/1...0d6829ef_c.jpg

But, after scraping down to metal, & re-installing ... nothing changed:
https://c1.staticflickr.com/9/8635/1...0c42c504_b.jpg

I have nominally 90VAC (actually 102VAC) on the flame sensor, but,
0.00ua of current is flowing across the flame to ground:
https://c4.staticflickr.com/8/7487/1...78da620b_b.jpg

What's that black jumper wire you have there that goes from the flame
sensor up to the top and out of the pic?

On Thursday, December 25, 2014 1:27:06 AM UTC-5, Danny D. wrote:
makolber wrote, on Wed, 24 Dec 2014 06:03:12 -0800:

OP, what kind of VOM do you have. Not all can read MICRO amps.
You would have to put the meter in series between the flame
sensor and the controller.

I have a Fluke 75, which can only get to around 1ma:
https://c4.staticflickr.com/8/7463/1...2757e870_b.jpg

However, I borrowed an Alpha 2360, which can read to 1/10ua.
https://c4.staticflickr.com/8/7487/1...78da620b_b.jpg

When I tested the AC voltage, I put a lead on ground and another
lead on the white wire from the control board to the flame sensor.

To test the DC current, I put one lead in the white wire from the
control board & the other lead on the flame sensor spade connector.

In that picture above, you can also see that I've added a black
jumper so that I could short the flame sensor to ground, in the
middle of the 7-second flame.

All I can say is:
a. The sensing of the flame failed.
b. The flame sensor is getting its nominal 90VAC from the control board.
c. There is no current whatsoever when measured in series with the flame
sensor using a meter capable of measuring 1/10ua.

Disregard my previous question about the black jumper wire.

I presume you measured continuity from the end of the sensor wire to
the electrode?

IDK how much you can see, but can you see that the flame sensor is
in the flame, ie that the flame is uniform, OK at the sensor?

Did you try testing the meter with some other small current load, to
make sure it doesn't have a blown fuse, etc?

The only thing I can add from all this is that given that you're measuring
normal voltage from the board to the sensor, then the possibility of a
bad ground would seem to be eliminated.

About the only thing left would be that we don't understand the
failure mechanism with the flame sensors. The few descriptions I read,
the physics were not well described. I wonder if it's possible something
changes on the surface of the metal over time, heating, etc that
causes it to stop working? I guess we'll find out when the new one
shows up. But given all that you've found so far, my vote would still
be the sensor. You apparently have 100V on it, no current flowing.

Regarding the current, I know it's supposed to be a few uA. But
I wonder how they define that? Peak? RMS? If it's peak, then it's
going to be substantially less RMS, because remember the flame rectifies
it, so you only have a half-wave, so you have two adjustments to get to
RMS. One that it's a sinewave, the other that it's only half of a sine
wave.

On 12/25/2014 6:02 AM, trader_4 wrote:
On Wednesday, December 24, 2014 11:45:30 PM UTC-5, Danny D. wrote:

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.

You didn't get the tank filled with non-conductive propane, instead
of the conductive kind, did you?


It's like ethanol gas, the old stuff is so
hard to find now days. Causes more problems.

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

Danny D. wrote:
Stormin Mormon wrote, on Mon, 22 Dec 2014 11:26:40 -0500:

With that clogged air filter, I'd be thinking bad thermal limit switch.
I replaced one this year in my own furnace, and one about a week later
for a customer.

Partial success!

After all the fiddling, I'm finally getting the thermal igniter to
ignite, and the flames go on three times, and then shut off, so,
that's a partial success, I guess.

First, the LED was solid red for a minute or so:
https://www.flickr.com/photos/98287134@N02/16082030575/

But then, it quickly switched to what appeared to be a code #12:
https://www.flickr.com/photos/98287134@N02/16081998125/

Then, the flames went on three times and then off within seconds
with a resulting LED blinking code of what appears to be #34:
https://www.flickr.com/photos/98287134@N02/16081950225/

Given all those inconsistencies within the span of 15 minutes,
I'm not sure if things are changing or if there are more than
one problem or if the thing just needs to settle down, because
those blink codes are changing depending on what is happening
with the blower.
https://c4.staticflickr.com/8/7505/1...4f42e6c5_c.jpg

The gas valve is definitely turned on, and there is plenty of
gas on the stove and in the 500 gallon propane tank.
https://c4.staticflickr.com/8/7508/1...4311f464_k.jpg

I will doublecheck that the metal case is grounded, and, I will
sand or steel wool the flame sensor and check the amperage if my
Fluke 75 can get down that low.

34: Ignition proving failu Control will try three more times
before a lockout #14 occurs. If flame signal lost after trial
for ignition period, blower will come on for 90-second
recycle delay. Check for:
- Oxide buildup on flame sensor (clean with fine sandpaper)
- Proper flame sense microamps (0.5microamps DC minimum)
- Gas valve turned off (manual shutoff valve, low inlet gas pressure)
- Green wire MUST be connected to furnace sheet metal
- Inadequate flame carryover or rough ignition

14: Ignition Lockout: Control will auto-reset after three hours.
Refer to #34.

12: Blower on after power up: (115V or 24V) Blower runs for 90
seconds, if unit is powered up during a call for heat
(R-W closed).
https://c4.staticflickr.com/8/7545/1...d3f7f629_c.jpg
Hi,
That is typical scenario when flame sensor does not do it's job.
Did you happen to check DC voltage(5V) the logic needs? One time
there was a TSB out on those board. One high Wattage resistor
overheating causes resistor lead solder joints on the board crack
causing all kinda funnies. I had to reinforce the joints with lots of
solder and drill holes on plastic cover. In a situation like that
multimeter often can't catch intermittent glitches. O'scope is only way
to visualize it. Nowadays there is pocket size basic digital scopes.
Sensor rod shoild be positioned right in the flame.

On 12/25/2014 1:15 AM, Danny D. wrote:
In this picture below, the left flame sensor is the bottom
one that I cleaned of rust, down to the bare metal.
https://c4.staticflickr.com/8/7547/1...41d3cfc5_b.jpg

It didn't make any difference.


Some thing called a flame spreader, which
metal channel goes from burner to burner. Been
a while since I had one of them apart.

At the risk of sounding like a grinch, I'm so
completely tired of that ## furnace. Of course,
I've been sick for a couple days, and not my
usual cheerful self.

-
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

Tony Hwang wrote, on Thu, 25 Dec 2014 07:50:31 -0700:

Did you happen to check DC voltage(5V) the logic needs?

I don't know where to look for that 5VDC yet.

there was a TSB out on those board.

I don't know where to find a TSB.

All I know about the board is that it has this number on it:
1012-940-J HK42FZ009
https://c4.staticflickr.com/8/7517/1...15b36c3e_b.jpg

And one supplier told me the replacement is this:

325878-751 control board conversion kit.

Sensor rod shoild be positioned right in the flame.

The LH680014 flame sensor rod only goes in one way and it's
in the flame right in the middle, as can be seen on the bottom
burner of this picture, with the burner removed:
https://c4.staticflickr.com/8/7510/1...f06fc142_c.jpg

trader_4 wrote, on Thu, 25 Dec 2014 03:32:44 -0800:

Disregard my previous question about the black jumper wire.

MERRY CHRISTMAS!

I haven't seen that question about the black jumper wire yet, but, I
used it for two different purposes at two different times:
1. To ensure a ground from the burner metal to a chassis ground bolt
2. To short out the flame sensor in the middle of a flame to test it
that would kill the flame immediately.

(Neither effort changed anything.)

I presume you measured continuity from the end of the sensor wire to
the electrode?

You know, I did *not* check that, and I should have, although it sure
looks nice and tight and clean. But, I will check that, although, in
effect, when I checked for the 90VAC voltage, that tested the wire.

IDK how much you can see, but can you see that the flame sensor is
in the flame, ie that the flame is uniform, OK at the sensor?

I can't see much with the burners in place, but with the burner
removed, the flame sensor is "in" the middle of the flame:
https://c4.staticflickr.com/8/7467/1...609d3825_c.jpg

Did you try testing the meter with some other small current
load, to make sure it doesn't have a blown fuse, etc?

This is a great idea, because the meter isn't mine, so I just
assumed it worked. The meter read 104VAC when I tested the flame
sensor wire to ground, but, that was with the leads in different
holes, and that would be different fuses.

So, it could be that the meter is blown, so, I will try to rig
up a micro-amp test of some sort. (I'd hate to open it up because
it's not mine, although if the fuse is blown, I'd replace it as
a courtesy to my friend).

The only thing I can add from all this is that given that you're measuring
normal voltage from the board to the sensor, then the possibility of a
bad ground would seem to be eliminated.

Do you think so?

But, didn't I make my own ground because I tested that AC voltage at
the white wire from the control board to the chassis ground?

So, if there was a bad ground back to the control board, didn't
I actually circumvent it with the second test lead?

I'm still confused how to test the control-board ground.

About the only thing left would be that we don't understand the
failure mechanism with the flame sensors.

Other than cleaning it, which I've done now with emery cloth,
I also can't imagine the thing ever failing. It's just too simple
and sturdy. So, while I am hopeful that the new sensor will solve
the problem, I don't really think it will.
https://c4.staticflickr.com/8/7559/1...0d6829ef_c.jpg

Regarding the current, I know it's supposed to be a few uA. But
I wonder how they define that? Peak? RMS?

All the videos I watched had no current with no flame and then
it went up to 4 or 5 ua in the flame, but none said how it was
measured.

I don't think the Alfa 2360 meter has a choice though, of average,
peak, or root-mean-square. It just has a 400ua scale:
https://c1.staticflickr.com/9/8611/1...aecc44dc_b.jpg

trader_4 wrote, on Thu, 25 Dec 2014 03:11:27 -0800:

What's that black jumper wire you have there that goes from the flame
sensor up to the top and out of the pic?

I used the black jumper for various purposes in the tests.

1. I used it to "double" the ground from the burner metal plate to
a chassis bolt at a green ground wire at the top of the chassis.

2. I used it to "short" the flame sensor to ground (with the nominally
90VAC white AC wire still connected to the flame sensor) to see if
that shut down the flames prematurely (which it should do in a
working circuit).

Neither attempt changed anything.