Viessmann VITOCAL 300-A Installation And Service Instructions Manual page 121

Control unit diagnostics
Message
U78 Room sensor HC1
U79 Room sensor HC2
U7A Room sensor HC3
U92 Collector sensor
U9A Collector sensor
UA6 Secondary pump
UA8 Pump heat. circuit 1 No volume flow in heat-
UA9 Heat pump
(cont.)
Cause
Break, room tempera-
ture sensor heating
circuit A1
Break, room tempera-
ture sensor heating
circuit M2
Break, room tempera-
ture sensor heating
circuit M3
Short circuit, Vitosolic
collector temperature
sensor
Break, Vitosolic collector
temperature sensor
No volume flow in the
secondary circuit (sec-
ondary pump stopped)
ing circuit A1 (circulation
pump stopped)
&
Safety high pressure
switch or motor protec-
tion switch in fan has
responded
&
Control high pressure
or low pressure switch
has responded eight
times or longer than
24 h
&
Refrigerant circuit con-
trol fault (controller for
electronic expansion
valve EEV)
&
Primary/secondary
temperature sensors
faulty
Troubleshooting
Measures
Check the sensor and re-
place if required (see
page 164 and 173)
Check the sensor and re-
place if required (see
page 164 and 173)
Check the sensor and re-
place if required (see
page 164 and 173)
Check the sensor and re-
place if required (see
Vitosolic installation and
service instructions)
Check the sensor and re-
place if required (see
Vitosolic installation and
service instructions)
Check circulation pump
and replace if required
Check heating circuit
pump in heating circuit A1
and replace if required
Scan further messages
("Message history" see
page 117), check volume
flow rates, check motor
currents/motor protection,
check safety high pressure
switch
Note
Switch appliance OFF and
ON after removing fault.
121