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VS8420 MILLIVOLT GAS VALVE
Disconnect power supply before making wiring
connections to prevent electrical shock or equipment
damage.
1. Check the power supply rating on the gas valve
and make sure it matches the available supply.
Install the transformer, thermostat, and other con-
trols, as required.
2. This valve can be used only in a self-generating
system.
TARGET
MILLIVOLT
THERMOSTAT
HIGH LIMIT
CONTROL
VS8420 HI/LO MILLIVOLT GAS VALVE
HI/LO
REGULATOR
PIEZO SPARKER
Fig. 7. Millivolt wiring system wiring diagram with
quick drop-out thermocouple (VS8420D).
69-1165—3
APPLY WRENCH
FROM BOTTOM OF
GAS CONTROL TO
SHADED AREA
Fig. 6. Proper use of wrench on gas valve.
Q313
THERMOPILE
QUICK DROP-OUT
THERMOCOUPLE
ELECTRODE
GAS
PILOT
CONTROL
ADJUSTMENT
KNOB
SCREW
M12678
3. Adjust the thermostat heat anticipator to the 0.1A
at 750 mV rating stamped on the valve operator.
OPERATION
The Millivolt Gas Valve System includes a gas valve,
quick drop-out thermocouple, thermopile, millivolt
thermostat and a pilot burner. In this configuration, the
thermopile drives the operator and the quick dropout
thermocouple operates the power unit. See Fig. 7.
As an option, a piezo can be mounted on the valve to
ignite the pilot burner. The piezo creates a spark when
the plunger is depressed. The connecting wires of the
piezo include a terminal to connect to the electrode of the
pilot burner. The piezo is replaceable.
Pilot Gas Lighting Procedure
Lighting Standard Pilot (Without Piezo)
1. Turn the knob counterclockwise
PILOT position, push the knob down, and hold in
position. The pilot valve opens and allows gas to
flow to the pilot burner.
2. Light the pilot burner while holding down the knob
until a strong flame is present (approximately 60
seconds).
3. Release the knob. The shaft will move upward and
engage the safety valve lever that opens the safety
valve.
4. Turn the knob counterclockwise
position. On a call-for-heat, the main valve opens
and the main burner ignites.
4
M12679
to the
to the ON
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