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Page
240 (T-H3J), 340 (T-H3S) and 540 (T-H3) models Service Manial
Ver. 1.00
CONFIDENTIAL
Error Code
Malfunction description
Cancellation method
121
Error code is shown
after three failed
attempts at ignition
Loss of flame
Turn off the power or water supply
Diagnosis
Check point
1 Check gas supply and pressure
(Refer to section 1)
2 PCB fault
[1] No voltage to gas main solenoid valve (MV)
Normal: 93 to 120 VDC between COM (blue) & #3 (light blue)
(during operation)
[2] No voltage to gas solenoid valve (SV
2
)
Normal: 93 to 120 VDC between COM (blue) & #53 (orange)
(during operation)
[3] No voltage to gas proportional valve (VG
0
)
Normal: 1.0 to 15 VDC between white & red (during operation)
C
H1
3 Gas solenoid fault
[1] Main gas solenoid valve (MV) fault
Normal: 1.35 to 1.65 kΩ between COM (blue) & #3 (light blue)
[2] Gas solenoid valve (SV
2
) fault
Normal: 1.35 to 1.65 kΩ between COM (blue) & #53 (orange)
[3] Gas proportional valve (VG
0
) fault
Normal: 1.0 to 15 VDC between white & red
C
H1
4 Check for soot on the flame rod
[1] Clean the flame rod
[2] PCB fault
During operation: more than 1 μA through the flame
rod wire (orange)
I
5 Disconnected/damaged O.H.C.F.
(Refer to section 10-16)
Visual inspection: connection/breakage of wires.
Normal: 1.0 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 10-14)
Visual inspection: connection/breakage of wires.
Normal: 1.0 Ω or less between blue & blue
C1
Error Code
Malfunction description
Cancellation method
311
Disconnected/short-circuited outlet thermistor
(Only 240 (T-H3J) / 340 (T-H3S) models)
Disconnected/short-circuited heat exchanger
thermistor (Only 540 (T-H3) models)
Turn off the power or water supply
Diagnosis
Check point
1 Outlet thermistor / Heat exchanger fault
(Refer to section 10-12)
Visual inspection: connection/breakage of wires and/or debris on
thermistor.
Check voltage/resistance between black & black (#113).
Refer to Section 8 (A) for proper range of values.
E1