A.O. Smith T-M50 ASME Service Manual page 41

Error Code
121
5 Disconnected/damaged O.H.C.F.
V isual inspection: connection/breakage of wires.
Error code is
Normal: 1 Ωor less between blue & blue
shown after
6 Check if hi-limit switch is properly functioning.
three failed
7 Disconnected/damaged hi-limit switch. (Refer to section 10-11)
attempts at
V isual inspection: connection/breakage of wires.
Normal: 1 Ω or less between blue & blue
ignition
Error Code
Disconnected/short-circuited output thermistor
311
1 Output thermistor fault
V isual 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.
Error Code
Disconnected/short-circuited inlet thermistor
321
1 Inlet thermistor fault
V isual 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.
Error Code
Disconnected/short-circuited mixing thermistor
331
1 Mixing thermistor fault
V isual inspection: connection/breakage of wires and/or debris on
thermistor.
Check voltage/resistance between black & black (#113).
Refer to Section 8 for proper range of values.
Diagnosis
Malfunction description
Diagnosis
Malfunction description
Diagnosis
Malfunction description
Diagnosis
41
T-M50 / T-M50 ASME Service manual
(Refer to section 10-12)
Cancellation method
Turn off the power or water supply
(Refer to section 10-10)
Cancellation method
Turn off the power or water supply
(Refer to section 10-10)
Cancellation method
Turn off the power or water supply
(Refer to section 10-10)
CONFIDENTIAL
Ver. 1.05
Checkpoint
C2
C1
Checkpoint
E2
Checkpoint
E3
Checkpoint
E1