A.O. Smith T-D2-OS Service Manual page 40

Error Code
5 Disconnected/damaged O.H.C.F.
V isual inspection: connection/breakage of wires.
111
Normal: 1 Ω or less between blue & blue
6 Disconnected/damaged hi-limit switch. (Refer to section 10-12)
V isual inspection: connection/breakage of wires.
Normal: 1 Ω or less between blue & blue
Error code is
7 Inspect flame rod
shown after
[1] Check for any soot on the rod.
three failed
[2] Check the connection of ground wire; make sure there is firm contact to
attempts at
the ground of the water heater.
(in this case, the wire is contacted to the manifold surface.)
ignition
[3] PCB fault
During operation: more than 1 μA through the flame rod wire (orange)
[4] Flame rod fault
During operation: more than 1 μA through the flame rod wire (orange)
8 Check if hi-limit switch is properly functioning.
Error Code
Loss of flame
121
1 Check gas supply and pressure
2 PCB fault
[1] No voltage to gas main solenoid valve (MV)
Error code is
Normal: 78 to 100 VDC between COM (blue) & #3 (light blue)
(during operation)
shown after
[2] No voltage to gas solenoid valve (SV
three failed
Normal: 78 to 100 VDC between COM (blue) & #53 (orange)
attempts at
(during operation)
ignition [3] No voltage to gas proportional valve (VG
Normal: 1 to 15 VDC between white & red (during operation)
3 Gas solenoid fault
[1] Main gas solenoid valve (MV) fault
Normal: 0.9 to 1.3 kΩ between COM (blue) & #3 (light blue)
[2] Gas solenoid valve (SV
Normal: 1.3 to 1.9 kΩ between COM (blue) & #53 (orange)
[3] Gas proportional valve (VG
Normal: 1 to 15 VDC between white & red
Malfunction description
) fault
2
) fault
0
T-D2-IN / T-D2-OS Service Manual
Diagnosis
(Refer to section 10-13)
Turn off the power or water supply
Diagnosis
(Refer to section 1)
)
2
)
0
40
CONFIDENTIAL
Ver. 1.00
Checkpoint
Cancellation method
Checkpoint
C2
C1
I
C
H1
C
H1