Viessmann VITOCAL 300-A Installation And Service Instructions Manual page 125

Control unit diagnostics
Message
!D3 Low pressure
¸D4 Control high press.
UE1 Ext. heat source
UE2 Fault lag heat p
¸FF New start
Further information regarding messages
Message Characteristics of the control unit and effects on the system
U10 ...
The control unit is operated with an outside temp. of -40 °C.
U18 ...
U20 ...
The control unit is operated with the temperature value of the
U28 ...
secondary return temperature sensor plus 5 K. The heat pump is
stopped (message UA9) if both temperature sensors (secondary
flow and return) are faulty.
U21 ...
The control unit is operated with the temperature value of the
U29 ...
secondary flow temperature sensor minus 5 K. The heat pump is
stopped (message UA9) if both temperature sensors (secondary
flow and return) are faulty.
U30 ...
The heat pump will not start.
U31 ...
U38 ...
U39 ...
(cont.)
Cause
Circulation volume in the
primary circuit too low,
heat pump faulty or
pressure sensor faulty
Air in the heating circuit;
secondary or heating
circuit pump blocked;
condenser contaminated
or pressure sensor
faulty
Fault on the external
heat source
Fault at the lag heat
pump in a cascade
Control unit restart
Troubleshooting
Measures
&
Check the radial fan and
shut-off facilities
&
Have heat pump tested
by a refrigeration engi-
neer
Note
Pressure switch resets
itself automatically
&
Vent the heating circuit
&
Check system pressure
&
Check the secondary
pump and heating circuit
pumps
&
Flush the heating circuits
Check external heat
source
Check the lag heat pump
display
No measures required
125