115
[A12] Heating, hot water heater error
No
Hydro unit
DN code setting
DN_6D2 = “0”
DN_6D3 = “0”
Replace backup heater
unit and safety valve
Check wiring construction
Ask repair of power supply
DN code setting
DN_6D2 = “0”
DN_6D3 = “0”
A12 abnormality detection
Correct wiring
No
(Backup heater NG)
Backup heater or
hot water
cylinder terminal has
AC220-240 V±10% =
(single phase type)
AC380-415 V±10% =
(3 phase type)
Yes
Yes
Yes
Restart
Operation starts under
10 ≤ TWI 20°C
Heater backup operation
Heating: Booster heater
Hot water supply: Hot water cylinder heater
After 1 hour since heater operation
started, neither TWI ≥ 15
°C
nor TTW ≥ 20
°C
is met
Freeze prevention control is detected once
No
Backup heater element
is conductive
No
Wiring connection
is normal
Yes
Replace hot water
cylinder heater
No
(Hot water cylinder heater NG)
Hot water
cylinder heater element
is conductive
Yes
Replace TWI or TTW
sensor
No
TWI, TTW sensor
characteristics are
normal
Yes
(Refer to hot water
cylinder guide)
Check water
heat exchange
control board
If defective, replace it
PC board
MCC-1753
MCC-1755
(Refer to Characteristic table on page 137)
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