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Check code
Check code name
Activation of water High-
temperature protection
[A05]
(H-HWM)
Is there any
water heater
connected with
H-HWM ?
YES
Is the water
heater working ?
YES
Is line heater
output signal
from H-HWM
(COM-S2) 0V ?
YES
External water heater trouble
H-HWM control P.C. board trouble
TWI (TA) sensor trouble
TWO (TC2) sensor trouble
NO
Is there the water
heater which is not
NO
connected with H-
HWM connected to
the same water piping
as H-HWM ?
Check the external water
heater
NO
Are characteristics
of TWI (TA) and TWO
(TC2) sensor
resistance normal ?
Is H-HWM ambient
temperature within the
use range ?
– 68 –
Cause
NO
YES
NO
YES
NO
YES
Replace TWI (TA) or
TWO (TC2) sensor.
Install H-HWM and water
pipes in the freeze-free
place.
Check H-HWM I/F P.C.
board.
Failure → replace
Check contact of the
relay
*Contact is normally
close.
Failure → replace
Check magnet switch of
line heater.
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Troubleshooting
