Viessmann VITOCAL 300-G Installation And Service Instructions Manual page 148

Troubleshooting
Messages
(cont.)
Message
System characteristics Cause
DB Refrigerant circuit 2
DC Low pressure 2
148
Refrigerant circuit fault,
heat pump stage 2
(type BWS):
■ Safety high pressure
switch has responded.
■ Compressor motor
protection (thermal
relay) has responded
■ If supplied:
separate compressor
motor protection has
responded
Low pressure fault, heat
pump stage 2
(type BWS):
■ Heat pump faulty
■ Primary pump faulty
■ Low pressure sensor
has reported a fault or
is faulty
Measures
■ Check flow and return
temperature sensors in
primary and secondary
circuits.
■ Check primary and sec-
ondary circuits for pres-
sure and throughput
(see also message A9).
■ Have heat pump tested
by a refrigeration engi-
neer.
The switching signal can
be tested at connection
214.2.
Note
After removing fault,
switch appliance OFF and
ON again once.
■ Have heat pump tested
by a refrigeration engi-
neer.
■ Check pressure gauge,
primary pump and shut-
off facilities.
■ Check low pressure
sensor, lead and EEV
PCB, and replace if
required.
The signal from plug aYH
can be tested at connec-
tion 214.3. (Delivered
condition: Jumper instal-
led between terminals
116.3/116.4). If a pres-
sure sensor is installed,
the signal must be contin-
uously active.