Viessmann VITOCAL 300-G Installation And Service Instructions Manual page 146

Troubleshooting
Messages
(cont.)
Message
System characteristics Cause
D3 Low pressure
D6 Flow switch
146
Low pressure fault, heat
pump stage 1
(type BW):
■ Heat pump faulty
■ Primary pump faulty
■ Low pressure sensor
has reported a fault or
is faulty
Well circuit flow switch
cannot detect a flow
Measures
■ 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 215.5. (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.
■ Check well pump.
■ Check primary circuit.
■ If no flow switch is
installed, insert a
jumper between X3.3/
X3.4.
The signal can be tested
at connection 216.3 or
across terminals X3.3/
X3.4.