Laars MASCOT LX, Service Manual

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Mascot LX Service Manual
This boiler uses “direct spark ignition” to light the burner
flame. The ignition system includes the spark rod, a
ground rod, and a flame sensor. See Fig. B16-1. To
light the burner, the SIT controller sends a high-voltage
current to the spark rod and opens the gas valve. A
spark jumps from the spark to the ground rod and lights
the gas. The flame heats the flame sensor. The flame
sensor generates a very small voltage (milli-Volts) to
confirm that the gas is burning. If for some reason the
flame sensor does not detect a flame within a very short
time, the controller triggers a lockout.
This section of the boiler should not require much main-
tenance or troubleshooting. Table B16-1 shows the volt-
ages you should see in the ignition system during normal
operation.
Electrical Shock Hazard
While the burner is lighting, the controller will generate a
high voltage between the spark rod and the ground rod.
Use care when working around these parts or taking test
readings.
Correct Clearances
To ensure easy and reliable firing, the clearance be-
tween the spark rod and the ground rod must be 3/16”
(5 mm). See Fig. B16-1.
Function Observe when Test points Should observe this voltage
Open gas valve Trying to light burner #4-6 on X2 on SIT
Y-BL wires to valve
24V AC
Creating spark Trying to light burner T2 on SIT High voltage, see next page
for test procedure
Flame sensor rod Burner is lit #10 on X3 on SIT to
ground
±30 microamps
Table B16-1 - Normal voltages in ignition system
Fig. B16-2 - Connections for spark rod and flame sensor
Flame
sensor
Spark
rod
Ground
rod
Clearance:
3/16” (5mm)
Fig. B16-1 - Correct clearance for spark rod
Spark rod
Ground rod
B16
Direct Spark Ignition