A.O. Smith T-M50 ASME Service Manual page 40

Error Code
7 Inspect flame rod
[1] Check for any soot on the rod.
111
[2] Check the connection of ground wire; make sure there is firm contact to
the ground of the water heater.
Error code is
(in this case, the wire is contacted to the manifold surface.)
[3] Fault of Left and/or Right PCB
shown after
During operation: more than 1 μA through the flame rod wire (orange)
three failed
[4] Flame rod fault (insulated resistance)
attempts at
During operation: more than 1 μA through the flame rod wire (orange)
ignition 8 Check if hi-limit switch is properly functioning.
Error Code
Loss of flame
121
1 Check gas supply and pressure
2 Fault of Left and/or Right PCB
[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] Fault of Left and/or Right PCB
During operation: more than 1 μA through the flame rod wire (orange)
Malfunction description
) fault
2
) fault
0
T-M50 / T-M50 ASME Service manual
Diagnosis
Turn off the power or water supply
Diagnosis
(Refer to section 1)
)
2
)
0
40
CONFIDENTIAL
Ver. 1.05
Checkpoint
Cancellation method
Checkpoint
I
C
H1
C
H1
I