Gas and Oil Home Heating Furnaces - HELP!!: Payne furnace : ignition proving failure (lockout)

model PG8DAA024050 (ADJA);
serial 1202A74928
code is saying : Ignition proving failure. Possible OXIDE BUILDUP on flame sensor or perhaps defective hot surface ignitor. HOW DO I FIND AND CLEAN flame sensor? or fix hot surface ignitor?
Any help will do!
thanks (Still cold in Michigan)
:(

The flame sensing rod is located in the burner area usually on the opposite end of the rack from the ignitor. It generally has one wire (most often white or yellow) going back to the ignition module & plugged on to a terminal marked "Sens" or something similar. The rod itself is simply a metal rod with a porcelain insulator. Remove the rod from the holder & clean it with scotch brite or fine steel wool.
The hot surface ignitor has two wires covered with a woven hi-temp insulation. If the flame lights then quits, the ignitor is not the problem. If there is no glow from the ignitor before the furnace locks out, good chance the ignitor is bad.

Ignitor had a crack in it (Small).
Thanks. The expansion from the repeated times the furnace has turned on eventually led to the crack.
Cleaned sensor some,....but it was in good shape.

I suggest you get and keep on hand a spare ignitor. I suggest this to anyone with hot surface ignition. They are usually easy to change & far cheaper than an after hours service call.