Originally Posted by gazunni
I took the furnace apart. When I pulled it some pieces of a hardened hornets nest came out.
Looked at the burner and igniter and both were in good condition except the connection on the igniter. The terminal and connector were corroded. Replaced the connector and cleaned up the terminal.
Put it all back together. And the SAME problem still occurred. After about the 5th attempt it finally latched in. Tried on and off several times and it continued to work. Next day, same problem.
Got a new igniter board and replaced same. It only took 5 minutes to remove the old and install the new one. Everything worked first time.
I expect the flame sensor module is intermittently faulty.
Hopefully by posting my journey it may help others.
Thanks for all the feedback and advice.
Flame sensor (flame proving) is via the Spark Electrode
When flame ignites it generates an AC current in the flame. This current is rectirifed into a DC vurrent which circuit board senses via feedback thru spark electrode
Spark electrode is dual function
Provides high voltage spark for ignition via transformer on board and Orange wire
Provides feedback of millamp signal for flame proving..change in current is sensed by circuit board
Electrode must be clean (no soot/carbon)
Electrode wiring & connections must be clean/tight
Electrode ceramic can NOT have any cracks or wire be loos inside the ceramic
Ground (assembly mounting screw) must be clean/tight
4 wires on your circuit board
*White---12VDC coming from sail switch and high temp limit switch. Goes back to circuit board proving air flow is adequate----allows circuit board to send DC to gas valve/spark electrode
*Red---12VDC from circuit board to gas valve
*Blue---12VDC from thermostat to circuit board. Allows circuit board to send DC to FAN motor via blower circuit (which gets the DC via the power circuit from the On/Off CB)
*Yellow----Ground wire. Goes to terminal block with 12VDC Neg and motor ground