Toshiba HWT-602S21SM3W-E(TR) Service Manual page 128

[A08] Low pressure sensor operation failure
Start
Flow sensor is normal
Yes
Excess air
noise comes from
inside pump
No
circulation flow shortage
No
Flow rate
detected by flow sensor is
almost same as actual
value
Yes
Continued
operation at low outside
temperature and at 15°C or lower
set temperature
No
Defrosting
takes 15 mins or longer
(Frost remains)
No
Low pressure sensor
is normal
Yes
Check water
heat exchange
control board
If defective, replace it
No
Secure water
Yes
circulation amount
Yes
No
Yes
(Cooling overload operation)
Yes
No
PC board
MCC-1753
MCC-1755
Remove sufficiently
excess air
Waste stuck inside
water circuit
12 M or longer water
pipe to a branch,
or 5 or less branches
127
Replace flow sensor
Remove waste
Place buffer tank and
the second pump
Replace flow sensor
Raise set temperature
Defrost outdoor unit
where frost remains
Replace low pressure sensor