A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual page 48

Error Code
Fault of driving circuit for main gas solenoid
valve (MV, SV
510
(The computer checks the condition of the main
gas valve immediately after every operation and
the conditions of the solenoid valves 6 hours
after every operation)
1 PCB and/or main gas valve fault
(Refer to section 10-5 & 10-18)
V isual inspection of gas valves: connection/breakage of wires.
Normal: 78 to 100 VDC between COM (blue) & #3 (light blue)
(during operation)
Normal: 78 to 100 VDC between COM (blue) & #9 (green)
(during operation)
Normal: 78 to 100 VDC between COM (blue) & #53 (orange)
(during operation)
Normal: 78 to 100 VDC between COM (blue) & #73 (red)
(during operation)
V isual inspection of PCB: connection/breakage of wires and/or burn marks
on the computer board.
2 Gas solenoid valve fault (MV, SV
Error Code
Fault of driving circuit for any of the gas
solenoid valves (SV
551
(The computer checks the condition of the
solenoid valves 6 hours after every operation)
1 PCB and/or gas valve fault
V isual inspection of gas valves: connection/breakage of wires.
Normal: 78 to 100 VDC between COM (blue) & #9 (green)
(during operation)
Normal: 78 to 100 VDC between COM (blue) & #53 (orange)
(during operation)
Normal: 78 to 100 VDC between COM (blue) & #73 (red)
(during operation)
V isual inspection of PCB: connection/breakage of wires and/or burn marks
on the computer board.
2 Gas solenoid valve fault (SV
Malfunction description
, SV and/or SV )
1 2 3
Malfunction description
, SV , and/or SV
1 2
, SV
1
520 Indoor / 520 Outdoor Service Manual
Turn off the power supply
Diagnosis
, SV and/or SV )
1 2 3
)
3
Turn off the power supply
Diagnosis
(Refer to section 10-5 & 10-18)
, and/or SV )
2 3
48
CONFIDENTIAL
Ver. 1.00
Cancellation method
Checkpoint
Cancellation method
Checkpoint
C
C