I have been out of town for about a week but my wife reports that our 7-year old (or so) furnace is heating only intermittently. And all day today, it didn't light at all.
The filter is only a month old, so airflow is good. I removed and cleaned with steel wool the flame sensor. Then I checked the sequence of ops, which for this unit is (according to install manual): call for heat; run some pressure sensor checks; energize draft blower; while draft blower comes up to speed, the pressure switch contacts will engage and the ignitor warms up for approx. 20 seconds; gas valve energizes; flame sensor confirms that ignition has been achieved within the 4 second ignition trial period...and away we go.
Okay, in my case, the board and pressure switches click; the board sends power to the ignitor (which I read with a digital meter at 94.5v) for 17 sec, it DOES NOT GLOW at all; the gas valve opens for 4 seconds, and then closes; the board cuts voltage to the ignitor; and the main blower runs for about 3 mins until a the system tries to restart. After a few tries, the board fault light issues two flashes, the code for "External lockout, no. of retries exceeeded."
1) Is the ignitor bad, or the board? (Ignitor is a White-Rodgers 768-A silicon nitride "stick.")
2) If the ignitor is bad, did it go bad over time because voltage sent by board was too high?
I read the specs; this ignitor is rated for 80v. I also read that too much voltage can be caused by a bad system ground. I noticed that the 6" green wire that is attached to the ground screw inside the furnace's junction box is stripped, but not connected to anything. It appears it may have been attached at one time to the cabinet interior, or jammed into the cabinet door hinge. There is nothing else nearby it would have been connected to. So,
3) How is a ground usually achieved with the ground wire from the furnace's junction box?
Thanks for your help. Winter in Chicago with no heat while hubby travels = HOSTILE WIFE.
Edited by gregger77, 04 December 2011 - 02:23 AM.