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VS8521 VENTFREE MILLIVOLT GAS VALVE
OPERATION
The Ventfree Millivolt Gas Valve System is configured to
include a gas valve, ODS pilot burner, and a millivolt
thermostat. In the ODS pilot burner, the thermopile drives
the operator and the thermocouple operates the power
unit.
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 the electrode of the
pilot burner. The piezo is replaceable.
Refer to installation instructions for the piezo envelope
assembly (part no. 396079), form 69-1206.
MILLIVOLT
THERMOSTAT
HIGH LIMIT
CONTROL
HI/LO
REGULATOR
Fig. 6. Millivolt system wiring diagram
with ODS pilot burner.
Pilot Gas Lighting Procedure
Lighting Standard Pilot (Without Piezo)
1. Turn the knob counterclockwise to the 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 to the ON position.
On a call-for-heat, the main valve opens and the
main burner ignites.
69-1223—1
ODS PILOT
BURNER
VS8521 HI/LO
MILLIVOLT
GAS VALVE
GAS
CONTROL
KNOB
M10948
Lighting Pilot with Piezo
1. Turn the knob on the gas valve counterclockwise
to the PILOT position, push the knob down, and
hold in position. The pilot valve opens and allows
gas to flow to the pilot burner.
2. Push the plunger on the piezo until the pilot burner
is lit. Hold 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 to the ON position.
On a call-for-heat, the main valve opens and the
main burner ignites.
Fig. 7. The VS8521 ventfree millivolt
gas valve with piezo.
Shut off Procedure
1. To shut off the system, turn the knob
clockwise
closes the main gas and safety valves; however,
the power unit must drop out before the lighting
sequence can begin again. The VS8521 drops out
within 30 seconds.
2. To relight the pilot light, follow the steps in the Pilot
Gas Lighting Procedure section.
HI/LO Regulator
As you turn the HI/LO knob, the gas pressure changes.
1. Turn the knob clockwise
setting to increase gas pressure.
2. Turn the knob counterclockwise
LO setting to decrease gas pressure.
Minimum and maximum regulator settings vary for each
individual gas valve. Table 1 lists possible minimums and
maximums for gas valves. See gas valve label for actual
minimum and maximum ranges.
4
PIEZO
to the OFF position. This action
toward the HI
toward the
M10949
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