Toshiba HWS-803XWHM3-E Service Manual page 95

[A04] Error Freeze prevention control
When the outside temperature or inlet water temperature is low (approx. 20°C or lower) and the room load is large
(operation frequency rating), the freeze prevention control may be activated.
Operation restart
Perform
air vent
Excess air
inside pump
Yes
Chattering from
flow switch
exchanger board DP_SW11-1
heater terminal has
230ACV ( ± 23V)
heater element
is conductive
TC, TWO, TWI
sensor characteristics
Replace water heat
exchange control board
Start
Secure water
circulation amount
No
Yes
Circulation
flow shortage
No
Water heat
No
is ON
Yes
Backup
No
Yes
Backup
No
(Backup heater NG)
Yes
No
(Refer to Charasteristic table on page 122)
are correct
Yes
Dirt clogging
inside water circuit
(inside strainer, etc)
12 M or longer
water pipe to
a branch, or 5 or
less branches
Power is
No
connect to backup
heater terminal
Yes
94
Replace flow switch
Fit buffer tank and the
second pump
Set DP_SW11-1 to ON
Connect backup heater
power cable
Set heater breaker to ON
Check indoor wiring
Replace backup heater unit
Replace TC, TWO,
and TWI sensors