Danny D. wrote, on Fri, 19 Dec 2014 23:56:58 +0000:

It just started getting cold in California, so, the heater power
was turned on, and ... and ... and ... uh ... um ... no heat.
https://c4.staticflickr.com/8/7508/1...4311f464_k.jpg

Update!

The heater certainly hasn't been turned on in a year, and maybe
in two years (as last year was warm). I don't remember, but, anyway,
the problem first looked like a reverse wire but the code was
basically constantly blinking.

As far as I can tell, that just means whatever old code was in
there has been wiped from the memory, so, it just blinked
incessantly to tell us that.

Anyway, we narrowed the problem to the fact that the flame wasn't
sensed, and, that meant only one of three things:
1. Bad flame sensor
2. Bad ground for the flame sensor circuit (through the flame)
3. Bad control board sensing of the flame sensor circuit.

I cleaned the flame sensor to no avail.
Replacing the $20 flame sensor solved the problem!

It's amazing that a simple stainless steel rod could fail, but,
it apparently did! Who knows why or how.

The way the flame sensor works is that 90VAC (nominal) is sent
to the flame sensor, which is just a steel rod with a single
electrical connection. When there is a flame, electrons flow
from the steel rod to the chassis ground of the burners through
the flame (rectifying the 90VAC to DC). The flame sensor circuit
on the control board senses the 5ua of DC current, and keeps the
relays on which control the propane gas flow.

The moment the 5ua of current isn't sensed, the control board
shuts down the relays controlling the flame, which is what
was happening. So, there was nothing wrong with the furnace,
other than the flame wasn't being sensed.

With the new flame sensor, everything is working fine.
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

What is almost incompressible to me is HOW the flame sensor
failed. It wasn't dirty. It wasn't shorted. It's just a steel
rod! The ceramic wasn't visibly cracked. I just don't get it,
but, it is what it is.

On Wed, 31 Dec 2014 05:22:55 +0000 (UTC), "Danny D."
wrote:

Danny D. wrote, on Fri, 19 Dec 2014 23:56:58 +0000:

It just started getting cold in California, so, the heater power
was turned on, and ... and ... and ... uh ... um ... no heat.
https://c4.staticflickr.com/8/7508/1...4311f464_k.jpg

Update!

The heater certainly hasn't been turned on in a year, and maybe
in two years (as last year was warm). I don't remember, but, anyway,
the problem first looked like a reverse wire but the code was
basically constantly blinking.

As far as I can tell, that just means whatever old code was in
there has been wiped from the memory, so, it just blinked
incessantly to tell us that.

Anyway, we narrowed the problem to the fact that the flame wasn't
sensed, and, that meant only one of three things:
1. Bad flame sensor
2. Bad ground for the flame sensor circuit (through the flame)
3. Bad control board sensing of the flame sensor circuit.

I cleaned the flame sensor to no avail.
Replacing the $20 flame sensor solved the problem!

It's amazing that a simple stainless steel rod could fail, but,
it apparently did! Who knows why or how.

The way the flame sensor works is that 90VAC (nominal) is sent
to the flame sensor, which is just a steel rod with a single
electrical connection. When there is a flame, electrons flow
from the steel rod to the chassis ground of the burners through
the flame (rectifying the 90VAC to DC). The flame sensor circuit
on the control board senses the 5ua of DC current, and keeps the
relays on which control the propane gas flow.

The moment the 5ua of current isn't sensed, the control board
shuts down the relays controlling the flame, which is what
was happening. So, there was nothing wrong with the furnace,
other than the flame wasn't being sensed.

With the new flame sensor, everything is working fine.
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

What is almost incompressible to me is HOW the flame sensor
failed. It wasn't dirty. It wasn't shorted. It's just a steel
rod! The ceramic wasn't visibly cracked. I just don't get it,
but, it is what it is.

Congratulations on fixing the problem. However, from an education
point of view, your statement that the flame sensor is just a hunk of
stainless steel is NOT correct. Google "thermocouple" and see how
they work. The current does not go through the flame. It is
generated by two pieces of dissimilar metals creating a voltage which
then causes a tiny current to flow and be sensed. They can and do go
bad.

On 12/28/2014 8:36 PM, Oren wrote:

Think about Donner Pass over the mountains. Folks became cannibals to
survive. Ate members of their party that died from the elements.

https://en.wikipedia.org/wiki/Donner_Pass#Weather

"...The pass was named after a later group of California-bound
emigrants. In early November 1846 the Donner Party found the route
blocked by snow and was forced to spend the winter on the east side of
the mountains. Of the 81 emigrants, only 45 survived to reach
California; some of them resorted to cannibalism to survive."


Interesting question. The Wiki page totally did
not have this information. The Donner party was
a group of..... kind of people. What did
the Donner group have in common?

The Donners were travelling why?

I know.... does anyone else?

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

On 12/31/2014 12:01 AM, Danny D. wrote:
The house has three separate furnaces.
Two are down, and have been down for a couple of years.
We usually don't bother using them.

It rarely gets below freezing - maybe once a year or twice at most.
No snow (a dusting once every five years).

We use warm blankets. Lots of them!
The only problem is I'm soured on down.
I bought perhaps ten down blankets over the years, mostly at
Costco, and while they're soft, they tear and bunch up in the
wash, so much that I'm not going to buy down ever again.

We have goose feathers all over the house.

Thanks, didn't know. Hey, hope you can get
heat before you have to eat your grand kids.

So, the Bryant in question was ... uh.... the
last straw? Furnaces of a feather flock
together? One bad apple done spoil the whole
bunch?

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

On 12/31/2014 12:05 AM, Danny D. wrote:
Danny D. wrote, on Sun, 28 Dec 2014 02:41:33 +0000:

Did you get the new flame sensor in?
It's supposed to arrive on Tuesday due to the holidays.

Woo hoo! Who would have thought a stainless steel rod could fail!
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

The moment I put the new one in, the heater worked like a charm!
https://c4.staticflickr.com/8/7522/1...39c96820_c.jpg

The meter still read 0.0 microamps, so, I'm sure the fuse was
already blown before I got it!
https://c4.staticflickr.com/8/7563/1...5a45a263_c.jpg

You guys were right all along!

Thanks for the follow up. Good to know you at least
have "some" heat, now. I hope it's enough to keep
your house comfortable. No resorting to canibalism
for your family, this year.

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

On Wed, 31 Dec 2014 04:31:14 +0000 (UTC), "Danny D."
wrote in

Unfortunately, if you own a BMW, and if you do all your own work,
you're forced to learn a LOT about the thing.

Next time buy a Honda.

On Wednesday, December 31, 2014 12:06:02 AM UTC-5, Danny D. wrote:
Danny D. wrote, on Sun, 28 Dec 2014 02:41:33 +0000:

Did you get the new flame sensor in?
It's supposed to arrive on Tuesday due to the holidays.

Woo hoo! Who would have thought a stainless steel rod could fail!
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

The moment I put the new one in, the heater worked like a charm!
https://c4.staticflickr.com/8/7522/1...39c96820_c.jpg

The meter still read 0.0 microamps, so, I'm sure the fuse was
already blown before I got it!
https://c4.staticflickr.com/8/7563/1...5a45a263_c.jpg

You guys were right all along!

So, what's the logical conclusion here? That something changed in
the properties of the metal? That's about all that's left, isn't it?
The insulator isn't shorted, it had continuity from tip to wire, etc.....
Funny thing, in the limited reading I did about flame sensors, I didn't
see anything about the metal needing to be special. Only that it needed
to be clean and you cleaned it up with sandpaper or steel wool, etc.
I'm left wondering what the actualy failure was.

Good to hear you got it going though and good info for the future.

On 12/31/2014 12:22 AM, Danny D. wrote:

With the new flame sensor, everything is working fine.
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

What is almost incompressible to me is HOW the flame sensor
failed. It wasn't dirty. It wasn't shorted. It's just a steel
rod! The ceramic wasn't visibly cracked. I just don't get it,
but, it is what it is.


I've forgotten that information. But
still, results is what counts. I've
also replaced a couple sensor rods.

Now, on to the next repair. With 500
posts, 50 Flickr pictures, and 4,000
reply posts from the list.

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

On 12/31/2014 6:21 AM, Pat wrote:
....

Congratulations on fixing the problem. However, from an education
point of view, your statement that the flame sensor is just a hunk of
stainless steel is NOT correct. Google "thermocouple" and see how
they work. The current does not go through the flame. It is
generated by two pieces of dissimilar metals creating a voltage which
then causes a tiny current to flow and be sensed. They can and do go
bad.

Flame sensors of this type are _not_ thermocouples and indeed the
current is carried by the flame (actually ions produced by the
combustion process). Thermocouples are also used, but they're entirely
different.

It is correct, however, that the flame detector is quite a bit more than
just a chunk of SS...

http://www.gayesco.com/Prod_Flame_Rods.htm

--

On Wed, 31 Dec 2014 09:00:35 -0600, dpb wrote:

On 12/31/2014 6:21 AM, Pat wrote:
...

Congratulations on fixing the problem. However, from an education
point of view, your statement that the flame sensor is just a hunk of
stainless steel is NOT correct. Google "thermocouple" and see how
they work. The current does not go through the flame. It is
generated by two pieces of dissimilar metals creating a voltage which
then causes a tiny current to flow and be sensed. They can and do go
bad.

Flame sensors of this type are _not_ thermocouples and indeed the
current is carried by the flame (actually ions produced by the
combustion process). Thermocouples are also used, but they're entirely
different.

It is correct, however, that the flame detector is quite a bit more than
just a chunk of SS...

http://www.gayesco.com/Prod_Flame_Rods.htm
Thank you for the education. I was not aware of that type.

On Wed, 31 Dec 2014 08:14:38 -0500, Stormin Mormon
wrote:

On 12/28/2014 8:36 PM, Oren wrote:

Think about Donner Pass over the mountains. Folks became cannibals to
survive. Ate members of their party that died from the elements.

https://en.wikipedia.org/wiki/Donner_Pass#Weather

"...The pass was named after a later group of California-bound
emigrants. In early November 1846 the Donner Party found the route
blocked by snow and was forced to spend the winter on the east side of
the mountains. Of the 81 emigrants, only 45 survived to reach
California; some of them resorted to cannibalism to survive."


Interesting question. The Wiki page totally did
not have this information. The Donner party was
a group of..... kind of people. What did
the Donner group have in common?

The Donners were travelling why?

I know.... does anyone else?


http://mormonhistoricsites.org/wp-content/uploads/2013/05/NJ9.1_Dorius.pdf

On Wed, 31 Dec 2014 05:05:34 +0000 (UTC), "Danny D."
wrote:

Woo hoo! Who would have thought a stainless steel rod could fail!
https://c1.staticflickr.com/9/8565/1...6ed2ba81_b.jpg

The moment I put the new one in, the heater worked like a charm!
https://c4.staticflickr.com/8/7522/1...39c96820_c.jpg

Good job Danny.

Stormin Mormon wrote, on Wed, 31 Dec 2014 08:18:12 -0500:

Thanks for the follow up. Good to know you at least
have "some" heat, now.


Two out of three is pretty good, compared to 1 out of 3
before.

trader_4 wrote, on Wed, 31 Dec 2014 05:29:47 -0800:

I'm left wondering what the actualy failure was.

I am clueless.

Maybe cracked ceramic that only opened up under red
hot heating of the metal rod?

Even then, what's the failure mode?
It would just be easier for the electrons to get to
the chassis (which is what they're trying to do
through the flame).

I really do not understand the failure mode, especially
as this thing is clean as can be.

I wish I understood HOW it failed.

VinnyB wrote, on Wed, 31 Dec 2014 07:22:32 -0600:

Next time buy a Honda.

We don't do FWD. But a Toyota will work fine!

Pat wrote, on Wed, 31 Dec 2014 07:21:06 -0500:

your statement that the flame sensor is just a hunk of
stainless steel is NOT correct. Google "thermocouple"

We thought the same thing too... at first.

dpb wrote, on Wed, 31 Dec 2014 09:00:35 -0600:

indeed the
current is carried by the flame (actually ions produced by the
combustion process).

I find it interesting that the electrons flow, in effect,
backward, in the opposite direction of the flame, from the
stainless steel rod, along the flame, back to the burner
metal to ground.

On Wed, 31 Dec 2014 23:37:23 +0000 (UTC), "Danny D."
wrote:

trader_4 wrote, on Wed, 31 Dec 2014 05:29:47 -0800:

I'm left wondering what the actualy failure was.

I am clueless.

Maybe cracked ceramic that only opened up under red
hot heating of the metal rod?

Even then, what's the failure mode?
It would just be easier for the electrons to get to
the chassis (which is what they're trying to do
through the flame).

I really do not understand the failure mode, especially
as this thing is clean as can be.

I wish I understood HOW it failed.

My guess is the metal expands and opens a crack in the ceramic (not
visible). I've read about this on a gas grill and stove igniters.
Don't recall the details - sorry. I was hinting about it earlier in
the thread. Would that be a short to ground?

dpb wrote, on Wed, 31 Dec 2014 09:00:35 -0600:

the flame detector is quite a bit more than
just a chunk of SS...
http://www.gayesco.com/Prod_Flame_Rods.htm

PHYSICAL CONFIGURATION
1. The flame rod consists of a center electrode and an outer metallic sheath.
2. The electrode is isolated from the outer sheath by an insulating material.
3. The end of the flame rod, in the flame path, has a special high temperature
hermetic seal with a threaded adaptor which is connected to the center
electrode.
4. A high temperature sensing rod is attached to the threaded adaptor.

I'm confused.
Is the "outer sheath" the ceramic?
Or, is the outer sheath the stainless steel rod exterior?

On 12/31/2014 5:48 PM, Danny D. wrote:
dpb wrote, on Wed, 31 Dec 2014 09:00:35 -0600:

the flame detector is quite a bit more than
just a chunk of SS...
http://www.gayesco.com/Prod_Flame_Rods.htm

PHYSICAL CONFIGURATION
1. The flame rod consists of a center electrode and an outer metallic sheath.
2. The electrode is isolated from the outer sheath by an insulating material.
3. The end of the flame rod, in the flame path, has a special high temperature
hermetic seal with a threaded adaptor which is connected to the center
electrode.
4. A high temperature sensing rod is attached to the threaded adaptor.

I'm confused.
Is the "outer sheath" the ceramic?
Or, is the outer sheath the stainless steel rod exterior?

As it says, the center electrode is isolated from the outer metallic
sheath by the ceramic. IOW, it's a center rod in the center of a
ceramic insulator all surrounded by the outer case that you see. It's
not a "rod" at all but a composite assembly that looks solid from the
outside.

--

On 12/31/2014 5:45 PM, Danny D. wrote:
dpb wrote, on Wed, 31 Dec 2014 09:00:35 -0600:

indeed the
current is carried by the flame (actually ions produced by the
combustion process).

I find it interesting that the electrons flow, in effect,
backward, in the opposite direction of the flame, from the
stainless steel rod, along the flame, back to the burner
metal to ground.

The primary direction of current flow is determined by the relative
sizes of the two electrodes...iow, it's determined by the geometry of
the detector in relationship to the burner to set up the current flow as
desired.

I didn't find a readable text(*); perhaps the Robertshaw publication
will help some...

http://www.google.com/url?sa=t&rct=j...63_RevB_1.pdf&
ei=t6KkVL29G4qFyQSRw4KYAw&usg=AFQjCNEdbUKV1Mm-cBkT8B4Ui1HGDtt9xg

(*) And, while am a MS Physics guy, I'm not going to try because I find
as soon as I do I end delving far too deeply and confound rather than
explain...

--

On Wednesday, December 31, 2014 8:14:03 PM UTC-5, dpb wrote:
On 12/31/2014 5:48 PM, Danny D. wrote:
dpb wrote, on Wed, 31 Dec 2014 09:00:35 -0600:

the flame detector is quite a bit more than
just a chunk of SS...
http://www.gayesco.com/Prod_Flame_Rods.htm

PHYSICAL CONFIGURATION
1. The flame rod consists of a center electrode and an outer metallic sheath.
2. The electrode is isolated from the outer sheath by an insulating material.
3. The end of the flame rod, in the flame path, has a special high temperature
hermetic seal with a threaded adaptor which is connected to the center
electrode.
4. A high temperature sensing rod is attached to the threaded adaptor.

I'm confused.
Is the "outer sheath" the ceramic?
Or, is the outer sheath the stainless steel rod exterior?

As it says, the center electrode is isolated from the outer metallic
sheath by the ceramic. IOW, it's a center rod in the center of a
ceramic insulator all surrounded by the outer case that you see. It's
not a "rod" at all but a composite assembly that looks solid from the
outside.

--

IDK what flame sensor you have there, but from the dimensions it looks
like it's a foot or more long, 1/2" in diameter and certainly not for a typical
home furnace. The one Danny has pics of does look like a small rod,
mounted on an insulator, connected to a wire. The descriptions I've
read about rod to flame conductivity also don't say anything special
about the reqts for the rod. They just say that a metal rod inserted
into a flame will conduct a current when voltage is applied. That would
seem to coincide with what he has, ie a metal rod on an insulator mount.

On 12/31/2014 7:52 PM, trader_4 wrote:
....

IDK what flame sensor you have there, but from the dimensions it looks
like it's a foot or more long, 1/2" in diameter and certainly not for a typical
home furnace. The one Danny has pics of does look like a small rod,
mounted on an insulator, connected to a wire. The descriptions I've
read about rod to flame conductivity also don't say anything special
about the reqts for the rod. They just say that a metal rod inserted
into a flame will conduct a current when voltage is applied. That would
seem to coincide with what he has, ie a metal rod on an insulator mount.

Those are commercial for larger boilers, etc., but the physics is the
same. There must be an isolated section for the current flow; otherwise
it would also be grounded. The _precise_ configuration is immaterial...

--

On Thursday, January 1, 2015 9:25:28 AM UTC-5, dpb wrote:
On 12/31/2014 7:52 PM, trader_4 wrote:
...

IDK what flame sensor you have there, but from the dimensions it looks
like it's a foot or more long, 1/2" in diameter and certainly not for a typical
home furnace. The one Danny has pics of does look like a small rod,
mounted on an insulator, connected to a wire. The descriptions I've
read about rod to flame conductivity also don't say anything special
about the reqts for the rod. They just say that a metal rod inserted
into a flame will conduct a current when voltage is applied. That would
seem to coincide with what he has, ie a metal rod on an insulator mount.

Those are commercial for larger boilers, etc., but the physics is the
same. There must be an isolated section for the current flow; otherwise
it would also be grounded. The _precise_ configuration is immaterial...

--

I agree. The isolated section is the metal rod with a wire attached.
It's housed in a ceramic insulator that holds it and keeps it isolated
from the furnace metal. The flame completes the circuit. The controller
board sends it a small current, at about 90V?. If the flame is there,
the controller detects that current is flowing, because the flame can
conduct a small current, it actually rectifies it. I had no idea how
this worked before, but that's what I learned from googling. I haven't
seen anything about any special requirements beyond that. And the pics
Danny posted of his flame sensors sure look like just a metal rod housed
in a ceramic insulator. So, from everything I've seen so far about
how it works, the physics, etc it sounds like just a metal rod.

So, if that's right, then the question remains, what failed in Danny's
detector? There have been so many posts, I'm unsure of is what exactly
he measured, what the readings were, etc.
I think he measured that there was infinite resistance between rod and
furnace metal, ie no shorting of the insulator. I think he verified
conductivity from end of wire to tip of rod, but not sure what exactly he
measured there. So, I don't understand what could be wrong with the old
one......

On 12/31/2014 12:09 AM, Danny D. wrote:
Stormin Mormon wrote, on Mon, 29 Dec 2014 10:01:01 -0500:

Danny will soon have to eat his grand kids to
stay alive?

We're still feeding them to fatten 'em up first!
https://c4.staticflickr.com/8/7522/1...f6b75fee_b.jpg


I'd eat Gretel first, Hansel can still
help fix the overhead deck you had blow
down.

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

On 01/01/2015 8:41 AM, trader_4 wrote:
....

So, if that's right, then the question remains, what failed in Danny's
detector? There have been so many posts, I'm unsure of is what exactly
he measured, what the readings were, etc.
I think he measured that there was infinite resistance between rod and
furnace metal, ie no shorting of the insulator. I think he verified
conductivity from end of wire to tip of rod, but not sure what exactly he
measured there. So, I don't understand what could be wrong with the old
one......

I'd guess the measurements he took aren't precise enough (or weren't
actually measuring what thought he was is also a possibility of course).

Being as it's a minute current, _any_ breakdown in the insulation and/or
hermetic seal could lead to having enough leakage current to essentially
short out the actual current but still measure a high (but not infinite)
impedance.

Hypothesis; we don't have enough info to be able to diagnose remotely
exactly. The key is it doesn't work; a new one does. That's good
enough for me...

In a "former life" was responsible for incore self-powered neutron
detectors for a particular commercial power reactor vendor. These are
essentially a current source also in the 100-1000 nano-amp range and are
a swaged leadwire on a Rh emitter surrounded by a ceramic in a metallic
sheath. (Sound familiar?)

Their OD is only about 1/16", the lead wire and ceramic are thus tiny.
Turned out that even though one could measure a very high bulk
resistance between the emitter and sheath that miniscule locations along
the length of the detector could have very localized thin spots and
become a shunt path for leakage currents. Also turned out that moisture
could infiltrate the end seal and gradually diffuse down the length of
the detector over time. This also reduced the overall resistance and
showed up as a systematically lower output signal but of great
variability as again the existence of the surface roughness and local
thickness made exponential changes in local conductivity.

The detectors had been tested for years at the corporate research
reactor without ever discovering the issues--turned out it required the
higher power density of the real thing for the issue to become
significant. While they're not identical, given the similarity in
construction and function I can imagine many such similar scenarios with
these devices. Mostly I imagine it is a moisture infiltration problem
with these as a first guess.

In the end, the reactor detector problems turned out to be a secondary
blessing; I got a MS thesis out of it while it kept me gainfully
employed to pay for the course work while working around the issues for
operating reactors w/o requiring warranty replacements and solving the
manufacturing problems for new product.

--

Oren wrote, on Wed, 31 Dec 2014 15:46:19 -0800:

My guess is the metal expands and opens a crack in the ceramic (not
visible). I've read about this on a gas grill and stove igniters.
Don't recall the details - sorry. I was hinting about it earlier in
the thread. Would that be a short to ground?

I just noticed this, so sorry for not responding sooner.
I'm still amazed that the heat sensor was bad, simply because there
was almost nothing to it.

I guess if, under heat, a crack allows electrons to "jump" to ground,
both ways, then the control board wouldn't measure any DC current
(because it would be AC). I'm guessing though.

trader_4 wrote, on Wed, 31 Dec 2014 17:52:16 -0800:

IDK what flame sensor you have there, but from the dimensions it looks
like it's a foot or more long, 1/2" in diameter and certainly not for a typical
home furnace. The one Danny has pics of does look like a small rod,
mounted on an insulator, connected to a wire.

The one I have is only a couple of inches long, and maybe
something like 1/8 of an inch in diameter of the rod itself.

trader_4 wrote, on Thu, 01 Jan 2015 06:41:52 -0800:

So, if that's right, then the question remains, what failed in Danny's
detector? There have been so many posts, I'm unsure of is what exactly
he measured, what the readings were, etc.
I think he measured that there was infinite resistance between rod and
furnace metal, ie no shorting of the insulator. I think he verified
conductivity from end of wire to tip of rod, but not sure what exactly he
measured there. So, I don't understand what could be wrong with the old
one......

All this is true.

I'm "guessing" that a crack developed in the ceramic that allowed electrons
to flow both ways to the metal chassis that the assembly was bolted to.

But that's just a guess.

UPDATE:

The heater has been working (although it has been almost 70 degrees
lately) just fine with the new flame sensor.

Apparently, this is what happened:

1. Heater wasn't working for so long that it "forgot" the prior
error code, so it was just blinking incessantly.

2. Eventually, the heater got around to blinking a code for a
bad flame sensor circuit.

3. The observation was the flames would light and then shut off
within seconds, four times, and then lockout would occur until
the power to the furnace was turned off and back on.

4. All measurements to determine whether the flame sensor was
broken had failed, mainly because 5uA is hard to measure and
because the meter I had borrowed must have a blown fuse.

5. However, replacing the flame sensor worked.

How the flame sensor failed is a mystery, as it clearly was not
tarnished (it was sanded with steel wool, emery cloth, and a file,
over subsequent attempts). The ceramic "looked" intact, but may
have developed a fault such as a crack.

The assumption is that the flame sensor failed, although the
only proof of that is that the new flame sensor worked as
soon as it was installed.

Thanks for all your help and advice.
Who knew that the flames form part of an electrical circuit!

If you really want to verify a bad flame sensor, wait till spring,
and put the bad one back in, and see if the problem comes back.

But wait till spring
Mark

makolber wrote, on Fri, 09 Jan 2015 18:16:08 -0800:

But wait till spring

On Sat, 10 Jan 2015 00:11:04 +0000 (UTC), "Danny D."
wrote:

5. However, replacing the flame sensor worked.

How the flame sensor failed is a mystery, as it clearly was not
tarnished (it was sanded with steel wool, emery cloth, and a file,
over subsequent attempts). The ceramic "looked" intact, but may
have developed a fault such as a crack.

The assumption is that the flame sensor failed, although the
only proof of that is that the new flame sensor worked as
soon as it was installed.

Thanks for all your help and advice.

Doesn't the flame sensor have a "special" metallic coating? Sanding
it off will damage the sensor?

Who knew that the flames form part of an electrical circuit!

I think my HVAC furnace has a safety feature. When the flame goes out
the gas shuts down the gas valve. Wonder if it via the sensor?

On Fri, 9 Jan 2015 18:16:08 -0800 (PST), wrote:

If you really want to verify a bad flame sensor, wait till spring,
and put the bad one back in, and see if the problem comes back.

But wait till spring
Mark

.... or wait until the new one fails and then try the old one

chuckle