Manifold Pressure Adjustment; Main Valve Solenoid Connections - A.O. Smith SERIES 120 Service Handbook

Manifold Pressure Adjustment

The main gas regulators are found beneath the silver or black cap screws. (Natural Gas
valves have silver caps; Propane valves have a black caps). Remove the caps to access
the outlet (manifold) pressure adjustment screw. IMPORTANT: Ensure that the outlet
pressure matches the manifold pressure that is listed on the water heater rating plate.
• Natural Gas valves are factory preset to 3.5 inches W.C. The full rate outlet pressure
range is between 3 and 5 inches W.C.
• Propane (LP) valves are factory preset to
range is between 8 and 12 inches W.C.
• Caution: Always test the manifold pressure at the outlet when the gas is flowing.
Wiring Harness
Lead Wires
(24-Volt Main Valve
Solenoid Connections)

Main Valve Solenoid Connections

The figure above shows the two 24-volt main valve (MV) solenoid connections. The two
yellow wires from the 12-pin ignition board plug connect to these leads.
Servicing should only be performed by a Qualifi ed Service Agent
OPERATION AND SERVICE
10.0 inches W.C. The full rate outlet pressure
TOP VIEW OF GAS VALVE
Figure 13
17
Main Gas
Regulators
(Outlet Pressure
Adjustment)