Viessmann VITOCAL 242-G Installation And Service Instructions Manual page 128

Troubleshooting
Control unit diagnostics
Fault messages
BA KM BUS mixer
HC 2
BB KM BUS NC
mixer
BC KM BUS FB
HC 1
BD KM BUS FB
HC 2
C1 Power supply/
compressor
C4 Power-OFF
contact
C8 Safety chain
C9 Refrigerant
circuit
CA Primary pump
CB Primary tem-
perature
D0 Impressed
current anode
128
(cont.)
Cause
Communication fault mixer
HC 2
Communication fault nat-
ural cooling mixer
Fault KM BUS remote con-
trol; heating circuit 1
Fault KM BUS remote con-
trol; heating circuit 2
The compressor power
supply is not OK (e.g. rota-
tional direction, asymme-
trical, phase failure).
Compressor fuse, main
isolator, phase monitor or
motor overload faulty
Power-OFF contact en-
abled longer than 12 h
Fault at one of the con-
nected components
HP-LP or hot gas switch
Primary flow rate too low
or none present
Primary inlet temperature
below its minimum level
No impressed current
Measures
Check the extension kit
connections; start the ex-
tension kit
Check connections and
cables/leads
Check the power supply
and components; replace, if
required
Check the Power-OFF con-
tact; replace it, if required
External safety chain;
check connected compo-
nents and circuits (e.g.
brine pressure or jumper)
Check the flow and return
temperature sensors, test
the high pressure (see
page 117), check the pri-
mary and secondary circuits
for pressure and flow rate;
ask your local refrigeration
engineer to check the heat
pump, if required
Check the primary pump
(see page 115); replace, if
required
Check the brine circuit for
flow rate
Fill the DHW cylinder com-
pletely or check the im-
pressed current anode
contacts and the PCB; re-
place components, if re-
quired