Viessmann VITOTRONIC 200 Service Instructions Manual page 55

Messages
(cont.)
Message
Code/system characteris-
tics
B4 AD converter
Heat pump does not
start.
B5 EEPROM
Heat pump does not
start.
B7 KM BUS external unit
■ Compressor external
unit does not start.
■ Energy statement (see
page 91) will not be
calculated correctly.
Cause
Internal fault ADC (ana-
logue digital converter,
reference), ribbon cable
between sensor PCB
and main PCB faulty, or
PCBs faulty.
Internal fault, EEPROM.
Communication fault with
refrigerant circuit control,
external unit.
Troubleshooting
Measures
Check PCB; if required,
replace in the following
order: Controller and sen-
sor PCB (see page 172),
main PCB (see
page 150)
Note
After removing fault,
switch appliance OFF and
ON again once.
Replace coding card (see
page 172).
Check KM BUS connec-
tion. A fluctuating DC volt-
age between approx. 20
and 30 V must be applied
at:
■ Terminals X5.14 and
X5.15 on controller and
sensor PCB (see
page 172).
■ Terminal P501 on AVI
PCB (see page 176).
Check KM BUS connect-
ing cables of both PCBs;
check power supply to
PCBs; replace PCBs if
required.
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