Stormin Mormon wrote, on Tue, 23 Dec 2014 14:45:50 -0500:

Sorry, I knew you'd not get it. I ought not wrote that.

No problem. I had guessed that you might have been alluding to
a situation where a conclusion would be reached without the
scientific logic behind that conclusion.

While a *lot* of people just throw parts at a problem, and
even more make inferences that have no basis in fact, I
"try" to make logical inferences, and I try to test the fact.

I'm not always right, and, in fact, I'm often wrong; but in
the end, the item gets fixed, usually by fixing the right part.

In this case, I "may" have to throw parts at the problem,
because every test I "can" do on the flame sensor circuit
shows a good sensor, yet, clearly, the flame sensing circuit
is not working.

I contacted at least 5 distributors today, and only two
would sell a consumer parts. One had the flame sensor for
$20, the other for $18, but the $20 lady called first, so
I ordered over the phone. Since she didn't require an up-front
payment, I presume she has ordered it by now, so, I'll buy it
from her anyway.

She had the control board for $450, while the other guy had it
for $250, so, that's a bigger difference. I spent a few hours
(literally) on my side, in the crawlspace, staring at that
darn furnace, reading the three PDFs, staring at that darn thing
some more, and, like an idiot, turning it on over and over and
over again (even disassembling and reassembling the burners).

In the end, I gave up on debugging further.
a) I can't definitively test the flame sensor (I can't even figure
out yet how it works)
b) It's either the flame sensor or the motherboard, and,
c) If it's a ground, I can't find it.

https://c4.staticflickr.com/8/7540/1...7fc30d88_c.jpg