makolber wrote, on Tue, 23 Dec 2014 07:05:32 -0800:

it is difficult to measure the 5 uA using a VOM.

This guy tests the flame sensor in situ with an ammeter:
https://www.youtube.com/watch?v=OsIkK3AH1p4

The current for a good flame sensor starts at 0ua with no flame,
and then, with flame the ammeter reads 4ua.
https://www.youtube.com/watch?featur...3AH1p4#t=13 2

He mentions that a dirty flame sensor will read lower
current, so, now I know at least which direction the
thing goes.

a. There is no current when the sensor is cold.
b. There is low current when the sensor is dirty.
c. There is a handful of microamps when it's hot.

This guy removes the flame sensor and checks continuity
all along the stainless steel rod, using a technique
I have never seen before for a metal (conductive) rod:
https://www.youtube.com/watch?featur...mnKXZLzzs#t=18

Here they hook up a Fieldpiece HS36 ammeter into the flame
sensor in series,
https://www.youtube.com/watch?featur...BbZvpg#t=36 5

They had a reading of 0ua when cold, 2ua when dirty, and 3ua
when cleaned. The difference between not working and working was
only 1ua, so, a bad ground would certainly affect microamps!