A.O. Smith T-D2-OS - Page 41

T-D2-IN / T-D2-OS Service Manual
Ver. 1.00
41
CONFIDENTIAL
Error Code
Diagnosis Checkpoint
121
Error code is
shown after
three failed
attempts at
ignition
4 Check for soot on the flame rod
[1] Clean the flame rod
[2] PCB fault
During oper
ation: more than
1
μA through the flame rod wire (orange)
I
5 Disconnected/damaged O.H.C.F. (Refer to section 10-13)
Visual inspection: connection/breakage of wires.
Normal: 1
Ω
or less between blue & blue
C2
6 Check if hi-limit switch is properly functioning.
7 Disconnected/damaged hi-limit switch. (Refer to section 10-12)
Visual inspection: connection/breakage of wires.
Normal: 1 Ω or less between blue & blue
C1
Error Code
Malfunction description Cancellation method
311
Disconnected/short-circuited output thermistor Turn off the power or water supply
Diagnosis Checkpoint
1 Output thermistor fault   (Refer to section 10-11)
Visual inspection: connection/breakage of wires and/or debris on
thermistor.
Check voltage/resistance between black & black (#12).
Refer to Section 8 for proper range of values.
E2
Error Code
Malfunction description Cancellation method
321
Disconnected/short-circuited inlet thermistor Turn off the power or water supply
Diagnosis Checkpoint
1 Inlet thermistor fault (Refer to section 10-11)
Visual inspection: connection/breakage of wires and/or debris on
thermistor.
Check voltage/resistance between black & black (#42).
Refer to Section 8 for proper range of values.
E3
Error Code
Malfunction description Cancellation method
331
Disconnected/short
-
circuited mixing thermistor
Turn off
the power or water supply
Diagnosis Checkpoint
1 Mixing thermistor fault   (Refer to section 10-11)
Visual inspection: connection/breakage of wires and/or debris on
thermistor.
Check voltage/resistance between black & black (#113).
Refer to S
ection 8 for proper range of values.
E1