A.O. Smith T-M50 ASME Service Manual page 42

Error Code
Disconnected AFR rod
391
1 AFR rod fault
V isual inspection: connection/breakage of wires, soot on it.
Error Code
Flow sensor failure
441
1 Flow sensor failure
V isual inspection: connection/breakage of wires and/or debris on impeller.
Check voltage/resistance between (red & black) or (white & black)
Error Code
Fault of driving circuit for main gas solenoid
valve (MV)
510
(The computer checks the condition of the main
gas valve immediately after every operation)
1 Left and/or Right PCB and/or main gas valve fault
(Refer to section 10-4 & 10-14)
V isual inspection of gas valves: connection/breakage of wires.
Normal: 78 to 100 VDC between COM (blue) & #3 (light blue)
(during operation)
V isual inspection of PCB: connection/breakage of wires and/or burn marks
on the computer board.
2 Main gas valve fault
Malfunction description
Malfunction description
Malfunction description
T-M50 / T-M50 ASME Service manual
Turn off the power or water supply
Diagnosis
(Refer to section 10-6)
Turn off the power or water supply
Diagnosis
(Refer to section 10-9)
Turn off the power supply
Diagnosis
42
CONFIDENTIAL
Ver. 1.05
Cancellation method
Checkpoint
Cancellation method
Checkpoint
Cancellation method
Checkpoint
I
H2
C