Gas Valve - A.O. Smith Master-Fit 100 Series Service Handbook

GAS VALVE

The supply gas pressure is normally measured at the gas valve inlet gas pressure tap, if available, when the
gas is flowing. The manifold gas pressure is measured at the manifold pressure tap of the gas valve when
the gas is flowing. Gas valves used are 24 volt AC combination-step opening gas valves. They incorporate
the main valve and gas pressure regulator into one body. The inlet view of the gas valve shown on the left,
shows the Low Gas Pressure Switch, the Supply Gas Inlet, and the Supply Gas Pressure Tap.
The top view of the gas valve, shown on the right, shows the Main Gas Regulator, Manifold Pressure Tap, Top
Knob, and the Limited Bleed Vent Port. The main gas regulator is found under the silver cap (silver cap for
Natural Gas or black cap for Propane) screw. It is factory preset to 3.5 inches W.C. and adjusts gas pressure
output from 3.0 to 5 inches water column. Caution: Always test the manifold pressure at the outlet when the
gas is flowing.
The outlet view of the Gas Valve, shown on
the right, shows the Manifold Gas Outlet
Connection, the two 24 volt Main Valve (MV)
Solenoid connections, and the Manifold
Pressure Tap. The two yellow wires from
the 12-pin plug on the Ignition Board attach
to the MV terminals.
10 Servicing should only be performed by a Qualified Service Technician