A.O. Smith T-D2-OS Service Manual page 44

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