Toshiba HWS-P804XWHM3-E1(TR) Service Manual page 89

[A05] Error Piping freeze prevention control
Restart
TWI 4, TWO
THO 4 is detected
Circulation pump keeps
being energized or 3 minutes
passed after the start
Water heat
exchange control board
DPSW11-1 is ON
Backup heater terminal
has 220-230 V (± 10 %)
Backup heater element
is conductive
TWI, TWO, THO
sensor characteristics
are correct
Replace water heat
exchange control board
AMP Air Conditioning
4, or
No
Yes
No
Yes
Power is connect to
built-in heater terminal
No
(Backup heater NG)
Yes
No
(Refer to Characteristic table on page 113)
Yes
No
Yes
88
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Set water heat board
DPSW11-1 to ON
Place power cable for
backup heater
Set breaker for backup heater
to ON, or Check indoor
electronic wiring
Replace backup heater
and safety valve
Replace TWI, TWO,
and THO sensors