Viessmann Vitocal 350-A Installation And Service Instructions Manual page 150

Troubleshooting
Control unit diagnostics
Message
System characteristics Cause
¸D4 Control high press
«E0 LON subscriber
«E1 Ext. heat source
«E2 Fault lag heat p
¸FF New start
150
(cont.)
High pressure fault
■ Air in heating circuit
■ Secondary pump or
heating circuit pump
stalled
■ Condenser contamina-
ted
■ High pressure sensor
faulty
LON subscriber has
failed or connection
faulty.
Fault - external heat
source
Fault at a lag heat pump
in the cascade
Heat pump control unit
restart
Measures
■ Vent heating circuit.
■ Check system pres-
sure.
■ Check secondary pump
and heating circuit
pumps.
■ Flush heating circuits.
Note
In rare cases, e.g. during
DHW heating, a control
high pressure shutdown
can occur.
If this occurs several times
in succession, check heat
pump and configuration of
refrigerant circuit.
■ Call up fault memory at
faulty subscriber.
■ Check address (system
and subscriber num-
bers); check connec-
tions and LON connect-
ing cables.
Check external heat
source.
Check heat pump control
unit display at lag heat
pump.
No measures required.