1.Check for 24 volts at the spark ignitor from the ignition control board (ICB). Check the
2.Check the ground wiring for the ICB and the gas valve is intact and making good electrical connection. Check the ceramic insulator on the spark ignitor for breaks or cracks. Replace the spark ignitor if damaged.
3.With the draft motor running, check for 24 volts at the pressure switch terminal on the ICB. If not present, check for 24 volts on the terminal from the pressure switch. If present, go to step 4. If 24 volts is not present, the either pressure or rollout switch is not closed. Or the draft motor is not sufficiently evacuating the heat exchanger tubes or the pressure switch has failed. Check the operation of the pressure switch. Check the line voltage to the unit; if line voltage is low, call the local power company. If the problem persists, the draft motor may need replacement.
4.If the furnace is hot, it may be out on a high temperature limit open; wait for limit reset.
5.If all are intact replace the ICB.
The draft motor runs and the spark ignitor sparks at the burner, but the burner does not ignite and a gas odor is not detected at the draft motor outlet.
1.Check to ensure gas is being supplied to the unit. Con- firm that the gas pressure to the unit is within the proper limits as described in the “POST START CHECKLIST”.
2.Check the voltage at the gas valve and at the gas valve terminals on the ICB. Check all wiring between the ICB and the gas valve. Check to make sure the ground con- nections are intact.
3.If 24 volts is present, remove the pilot burner and the ori- fice. The removal procedure is described in “BURNER/ORIFICE INSTRUCTIONS.” Inspect the ori- fice for obstruction. If it is clear, replace the gas valve.
Main burners light but exhibit erratic flame characteristics.
4.Check the main burner orifices for obstruction and align- ment. The removal procedure is described in “BURNER/ORIFICE INSTRUCTIONS.” Clean or replace burner orifices and burners as needed.
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