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B.
Diagnosis and Repair (continued)
3. The Electrode Assembly
Positioning of the electrode assembly is very important. The gap between spark and ground should
be 118" (see diagram below). The spark and ground probe should not be grounded to the flame
spreader or any other metal object in the combustion chamber. The sensing probe relays to the
circuit board a signal that a flame is present. This signal is a small DC current which can be
measured directly with a 0 to 50 microamp meter. Although the minimum flame current necessary
to keep the ignitor from going into lockout is 1.5 microamps, the meter readings should be 3.0
microamps or higher.
To measure flame current, first shut off the power to the system and then remove the flame sensing
lead wire from the electrode terminal and insert the microamp meter in series with the sensor
electrode and ground. "Plus" terminal of meter to component board and "negative" terminal to sensing
electrode. Energize the ignitor. If microamps too small, check the following:
a) Check for correct input polarity. Terminal 1 should be "hot" (12 volts DC) with respect to ground.
Terminal 6 is neutral, or zero voltage, with respect to ground.
b) Improper grounding
-
if a flame is present during the trial for ignition period but the system shuts
down, make sure the burner is properly grounded. If not, the system will go into lockout.
c) Check the electrode ceramic for cracks or carbon. Make sure the electrode is free form carbon
deposits and is not corroded or pitted.
d) Check electrode leads for corrosion at the terminals. If there is corrosion, clean it off.
e) Check the sensor wire continuity. If defective, replace it.
f) Re-position the electrode assembly and check the spark gap. If the gap is too wide, damage to the
ignitor can result.
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