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

GAS VALVE

The 24 Volt Gas Valve on the XB Boilers/XWH water heaters is AC voltage valve. The Control Board sends 24 VAC to the gas valve.
See Figure 6 on Page 14.
Gas Valve Voltage Test
• Check for 24 VAC supplied to the 24 Volt Gas Valve at pin 2 of the J5 Connector on the Control Board. Using an "AC" volt
meter connect one lead to pin 2 of the J5 Connector and the other lead to ground. 24 VAC should be present.
Gas Valve Removal:
The outlet of the 24 Volt Gas Valve is connected by flange directly to the side of the Venturi and is secured by four - 5/32" hex head
screws. A gasket is fitted into the gas valve's outlet flange. Ensure there is a new gasket on hand before removing the valve. Call the
toll free phone number on the back cover of this manual to order parts. Have the complete Model, Series and Serial number (located
on the boiler/water heater's rating label) for the boiler/water heater being serviced on hand before calling.
1. Turn off power to the boiler/water heater at the Main Power Supply switch.
2. Loosen the retaining screw for the wiring harness plug on the valve and disconnect the plug.
3. Turn off the supply gas to the boiler/water heater at the main gas shutoff valve.
4. Disconnect the supply gas line to the boiler/water heater at the boiler/water heater's 24 Volt Gas Valve.
5. If the boiler/water heater has been installed in a Direct Vent configuration, disconnect the intake air pipe at the intake air
connection on the boiler/water heater.
6. Remove the 4 gas valve mounting screws - 5/32" hex head screws.
7. Carefully lift the 24 Volt Gas Valve body off of the Venturi.
8. Follow these steps in reverse order to reinstall the 24 Volt Gas Valve.
9. Run the boiler/water heater through a complete cycle before leaving to ensure it is operating properly.
Gas Pressure
The boiler/water heater covered in this Service Manual is rated from 920,000 Btu/hr to 3,400,000 Btu/hr input. It is certified for
elevations up to 2000 feet (610 meters) for Propane and 10,100 feet (3079 m) for Natural gas. For higher elevations call the toll free
support phone number shown on the back cover of this manual for technical assistance.
Models
(XB/XWH)
Type of Gas
Natural
1000, 1300, 1700
2000, 2600, 3400
Propane
Service Notes:
• The manifold gas pressure is factory set and cannot be adjusted in the field.
• The manifold gas pressure and the supply gas pressure can be measured at two pressure test ports on the boiler/water
heater's 24 Volt Gas Valve. The manifold pressure test port is closest to the Combustion Blower. There is a needle valve in
each test port that is opened/closed with a small slotted screwdriver. Turn the needle valve counter-clockwise to open the test
port valve and clockwise to close it.
• Manifold gas pressure will run close to 0" W.C. or lower (in a vacuum) depending on the current operating state. This
pressure will be considerably lower, -0.2" W.C. to -4.9" W.C. during the Pre- Purge and Post-Purge operating states when the
Combustion Blower is running at high speed and the 24 Volt Gas Valve is closed.
• There is usually a drop in supply gas pressure noticed when the boiler/water heater's 24 Volt Gas Valve opens during ignition.
Seeing a corresponding rise in manifold pressure during ignition confirms the valve is opening and gas is flowing to the Burner.
• A sustained drop in supply gas pressure of 1.5" W.C. or more during boiler/water heater running may indicate the supply gas
line is undersized. If the boiler/water heater is experiencing a sustained drop in supply gas pressure of 1.5" W.C. or more and
the boiler/water heater is experiencing repeated Ignition Failure conditions, intermittent loss of flame or rough starting ensure
the supply gas line is sized in accordance with the current edition of National Fuel Gas Code (ANSI Z223.1/NFPA 54) or the
Natural Gas and Propane Installation Code (CAN/CSA B149.1).
TABLE 2. GAS PRESSURE
Manifold Pressure
Inches W.C.
Min Fire -0.2 to - 0.3 -0.05 to - 0.07
Max Fire -3.0 to -3.9 -0.75 to -0.97
Min Fire -0.1 to - 0.3 -0.025 to -0.07
Max Fire -3.6 to -4.9 -0.90 to -1.22
Servicing should only be performed by a Qualified Service Agent
Maximum Supply Pressure Minimum Supply Pressure
kPa Inches W.C.
14.0
14.0
kPa Inches W.C.
3.49 4.0
3.49 4.0
kPa
1.0
1.0
19