107
[A02] Temperature increase error (heating)
• If Boiler setting is ON (DN_6B0 is “1”) and DN_62 is “1” and actual boiler output is “ON”, the A02 error is not
detected.
Replace TWI, TWO,
and THO sensors
No
(TWI, TWO, THO ≥ 70°C)
TWI, TWO, and THO
sensor characteristics are
correct
Yes
No
Water outlet
temperature is 70
°C
or higher
Yes
Correct water circuit
(To prevent hot water of
other circuits from entering)
Yes
Hot water from
boiler or other circuits does
not come in
No
Failure of backup heater
(Too large heater input,
thermostat short circuit)
Replace heater unit
or
Check water heat exchange
control board
If defective, replace it
Yes
Backup heater is energized
No
(Measure heater current)
Start
Check water heat exchange control board
If defective, replace it
PC board
MCC-1753
MCC-1755
PC board
MCC-1753
MCC-1755
Yes
Flow
sensor is normal
No
Replace flow
sensor
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