Service Handbook - AO Smith Water Heaters

Gas Valve
The 24 Volt Gas Valve on these water heaters is DC voltage valve. The CCB sends 24 VAC to the valve and
the AC voltage is rectified into a DC voltage by electronics contained inside the plug end of the 24 Volt Gas
Valve wiring harness, see Figure 23 below.
24 VOLT GAS VALVE ASSEMBLY TOP VIEW
24 VOLT GAS VALVE WIRING
HARNESS PLUG. 24 VAC
FROM CCB IS RECTIFIED TO
24 VDC BY ELECTRONICS
INSIDE THE PLUG END.
VENTURI
24 VAC FROM THE J6 SOCKET
ON THE CCB CONNECTS TO
THESE TWO SPADE TERMINALS
AT THE END OF THE 24 VOLT
GAS VALVE WIRING HARNESS.
PLUG RETAINING
SCREW
24 VOLT GAS VALVE
SUPPLY GAS CONNECTION
24 VOLT GAS VALVE
WIRING HARNESS
COMBUSTION
BLOWER
Figure 23
Gas Valve Voltage Tests
1. Check for 24 VAC supplied to the 24 Volt Gas Valve at pins 2 and 15 of the J6 Plug on the CCB, see
CCB Cover Removal And Replacement on page 40 and CCB Circuit Board Layout on page 41. Using an
"AC" volt meter insert the two test probes into pins 2 and 15 of the J6 Plug on the CCB during the
Ignition Verification or Heating operating states, see Figure 24 below. 24 VAC should be present. The
animated gas valve Status Icon is displayed on the Control System LCD during these operating states.
See Operating States on page 48 and Desktop Screen on page 46.
2. Check for 24 VDC at the plug end of the 24 Volt Gas Valve wiring harness during the Ignition Verification
operating state. Loosen the retaining screw for the 24 Volt Gas Valve wiring harness plug and disconnect
the plug, see Figure 23 above. Lay the plug end upside down on a flat surface. Using an "DC" volt meter
insert the two test probes into the two outside plug sockets, see Figure 24 below. 24 VDC should be
present.
AC VOLTAGE TEST
DC VOLTAGE TEST
Figure 24
Servicing should only be performed by a Qualified Service Agent
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