LAARS Mighty Therm VW-PW (Sizes 175-400) - Installation, Operation and Maintenance Instructions - Manual (Page 28)

LAARS Heating Systems
Page 28
5.2.7 Testing the Fuse
To test the fuse:
1. Clip a lead of the voltmeter to the grounding
terminal.
2. Touch the other voltmeter lead to the 24VAC
terminal on the ignition control.
3. If there is no voltage, replace the fuse. A blown
fuse is usually an indication of a short in the
24VAC circuit. It is important that the cause of
the short be found and repaired. Do not jumper
or bypass the fuse.
5.2.8 Testing the Ignition Control
(for spark ignition)
Caution
The ignition control and igniter operate on 120V
power. Keep this in mind while servicing the heater,
and take care to avoid electrical shock.
The ignition control provides power to the pilot,
opens the gas valve when there is a call for heat, and
senses when a flame is established. To test the ignition
control for spark ignition:
1. Clip one lead from the voltmeter to the yellow
wire terminal on the transformer.
2. Touch the other voltmeter lead to the red 24V
terminal on the ignition control.
3. If the voltmeter reads voltage, the temperature
control and the manual reset hi-limit switch are
not keeping the heater from firing.
4. Make sure the pilot burner is positioned next to
the main burner (see Figure 38) and there is no
soot or dirt on it.
5. Make sure the electrode (part of pilot assembly)
is clean, the terminal connection is tight, and the
ceramic insulator lead is at least 3/8 inch (9.5
mm) from the heater chassis and other metal
parts.
6. Check for proper spark gap.
5.2.9 Testing the High Voltage
Ignition Lead
Connections must be tight, and silicone rubber
boots in place. Bare metal parts at the base of the
manifold bracket must be at least 3/8 inch (9.5 mm)
from other metal objects. To test the ignition lead:
1. Turn the control panel switch to on.
2. Make sure the temperature control is turned far
enough to call for heat. There will be a loud
clicking noise indicating the pilot electrode is
sparking.
3. If no sparking is heard, pull the ignition lead from
the ignition control and hold the bare terminal 1/8
to 3/16 inch (3.2 to 4.8 mm) from the ignition
stud with a pair of insulated pliers (see Figure
40).
4. If a spark does not jump the gap, replace the
ignition control.
NOTE: The ignition control cannot be repaired
in the field. If it does not operate properly, replace it.
5.2.10 Testing the Safety Shutoff
(for standing pilot)
After lighting the heater, test the ignition system
safety shutoff.
1. With the main burners firing, turn the gas valve
control knob off.
2. Turn power to the heater off.
3. Set the temperature control to its lowest setting.
4. Wait 5 minutes.
Caution
Flame Hazard. Failure to wait 5 minutes, or not
turning the gas valve knob to OFF, may cause the
flow of unlighted main burner gas.
5. Turn the gas valve control knob to the PILOT
position.
6. Without pressing the control knob down, it
should be impossible to light the pilot.
7. Relight the pilot following the lighting
instructions found on the inside of the heater.
8. Reset the temperature control.
9. Light the heater following the instructions found
on the inside of the heater.
5.2.11 Testing the Safety Shutoff
(for automatic pilot)
1. Find the red silicone rubber insulated wire that
runs from the pilot to the ignition stud on the
ignition control module.
2. With the main burners firing, use an insulated
pair of pliers to disconnect the sensor wire from
the control module. Do not pull on the wire. The
main burner flame should immediately go out.
3. Turn the gas valve control knob to the off
position.
4. Reattach the red silicone wire to the control
module.
5.2.12 Testing the Igniter Electrode
To test the igniter electrode:
1. Make sure all of the wire connections on the
ignition control and the gas valve are tight.