A.O. Smith 710 ASME Service Manual page 39

Error Code
6 Disconnected / damaged hi-limit switch. (Refer to section 10-11)
V isual inspection: connection / breakage of wires.
111
Normal: 1 Ω or less between blue & blue
7 Inspect flame rod
Error code is
[1] Check for any soot on the rod.
[2] Check the connection of ground wire; make sure there is firm contact to
shown after
the ground of the water heater.
three failed
(in this case, the wire is contacted to the manifold surface.)
attempts at
[3] PCB fault
During operation: more than 1 μA through the flame rod wire (orange)
ignition
[4] Flame rod fault
During operation: more than 1 μA through the flame rod wire (orange)
8 Check if hi-limit switch is properly functioning.
Error Code
Loss of flame
121
1 Check gas supply and pressure
2 PCB fault
[1] No voltage to gas main solenoid valve (MV)
Error code is
Normal: 78 to 100 VDC between COM (blue) & #3 (light blue)
(during operation)
shown after
[2] No voltage to gas solenoid valve (SV
three failed
Normal: 78 to 100 VDC between COM (blue) & #53 (orange)
attempts at
(during operation)
ignition [3] No voltage to gas proportional valve (VG
Normal: 1 to 15 VDC between white & red (during operation)
3 Gas solenoid fault
[1] Main gas solenoid valve (MV) fault
Normal: 0.9 to 1.3 kΩ between COM (blue) & #3 (light blue)
[2] Gas solenoid valve (SV
Normal: 1.3 to 1.9 kΩ between COM (blue) & #53 (orange)
[3] Gas proportional valve (VG
Normal: 1 to 15 VDC between white & red (during operation)
4 Check for soot on the flame rod
[1] Clean the flame rod
[2] PCB fault
During operation: more than 1 μA through the flame rod wire (orange)
Malfunction description
) fault
2
) fault
0
710 / 710 ASME Service Manual
Diagnosis
Turn off the power or water supply
Diagnosis
(Refer to section 1)
)
2
)
0
39
CONFIDENTIAL
Ver. 1.00
Checkpoint
Cancellation method
Checkpoint
C1
I
C
H1
C
H1
I