Lennox LGM Series Manual page 35

11-Spark Electrodes
An electrode assembly is used for ignition spark. Two iden­
tical electrodes are used (one for each gas heat section).
The electrode is mounted through holes on the left‐most
end of the burner support. The electrode tip protrudes into
the flame envelope of the adjacent burner. The electrode
assembly is fastened to burner supports and can be re­
moved for service without removing any part of the burners.
During ignition, spark travels through the spark electrode
(figure 25) and ignites the left burner. Flame travels from
burner to burner until all are lit.
The spark electrode is connected to the ignition control by a
8 mm silicone‐insulated stranded high voltage wire. The
wire uses 1/4" (6.35 mm)female quick connect on the elec­
trode end and female spark plug-type terminal on the igni­
tion control end.
NOTE-IN ORDER TO MAXIMIZE SPARK ENERGY TO
ELECTRODE, HIGH VOLTAGE WIRE SHOULD
TOUCH UNIT CABINET AS LITTLE AS POSSIBLE.
.125" ± .015"
ELECTRODE
(3.2 mm ± .4 mm)
GROUND
ELECTRODE
FIGURE 25
12-Flame Sensors
A flame sensor is located on the right side of each burner
support. The sensor is mounted through a hole in the burn­
er support and the tip protrudes into the flame envelope of
the right most burner. The sensor assembly is fastened to
burner supports and can be removed for service without re­
moving any part of the burners.
When flame is sensed by the flame sensor (indicated by mi­
croamp signal through the flame) sparking stops immedi­
ately. During operation, flame is sensed by current passed
along the ground electrode (located on the spark elec­
trode), through the flame and into the sensing electrode.
The ignition control allows the gas valve to stay open as
long as a flame signal (current passed through the flame) is
sensed.
GROUND
Page 35
SENSOR
FIGURE 26