Girard Products GSWH-1 Service Manual page 25

Gas Modulator Valve
Coil resistance should be between 40 and 50 ohms.
The orange (1K system) or white (2.2K system) wire on the gas
modulator valve coil is 12 VDC + supplied directly from the gas
modulator board. The black wire is chassis ground.
As the voltage increases the valve decreases the amount of gas flow
through the gas modulator valve decreasing the output BTU's and
decreasing the temperature rise.
Gas Solenoid Control
The gas solenoid valve is a dual
redundant valve. Coil resistance between
30 and 50 ohms.
Modulator Control Board Valve
The control board is located on the back
of the water heater. The red wire to the
gas modulator control board supplies
+12 VDC. The red wire attaches to
one of the brown power wires at the
gas solenoid valve. Power will only be
supplied to the gas modulator board
when the main pc board is powering
the gas solenoid control valve. When
the resistances of the temperature
dial decreases the voltage to the gas
modulator valve increases.
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