A.O. Smith T-D2-OS - Page 44

T-D2-IN / T-D2-OS Service Manual
Ver. 1.00
44
CONFIDENTIAL
Error Code
Malfunction description Cancellation method
701
1 PCB fault
[1] Fault of preparation for the mixing thermistor
operation.
[2] Fault of driving circuit for Gas Proportional
Valve(VG
0
)
Turn off the power or water supply
Diagnosis Checkpoint
1 Check the PCB and/or gas proportional valve
(Refer to section 10-4 & 10-15)
Visual inspection PCB: connection/breakage of wires and/or burn marks on
the computer board.
Visual inspection gas proportional valve: connection/breakage of wires of
the gas proportional valve.
Normal: 20
to
40
Ω between (white) & (red)
H1
Error Code
Malfunction description Cancellation method
721
False flame detection
Turn off
the power or water supply
Diagnosis Checkpoint
1 False flame detection (5 sec.)
Flame rod (Insulated resistance) fault
I
Error Code
Malfunction description Cancellation method
741
Miscommunication between water heater and
temperature remote controller
Restoring proper cable connections
between the water heater and the
Remote controller (TM-RE30). When the
computer detects proper connections
between the water heater and the
remote controller, "741" error code will
cease to display.
Diagnosis Checkpoint
1 Temperature remote controller (TM-RE30) or PCB fault
2 Check for signs of power surges.