Viessmann VITOCAL 300-A Installation And Service Instructions Manual page 126

Troubleshooting
Control unit diagnostics
Message Characteristics of the control unit and effects on the system
U40 ...
Mixer heating circuit M2 is closed.
U48 ...
U41 ...
Mixer heating circuit M3 is closed.
U49 ...
U50 ...
The control unit is operated with the temperature value of the
U58 ...
lower cylinder temperature sensor. DHW heating is blocked if
only one sensor is available or both sensors are faulty.
U52 ...
The control unit is operated with the temperature value of the
U5A ...
upper cylinder temperature sensor. DHW heating is blocked if
only one sensor is available or both sensors are faulty.
U60 ...
The buffer cylinder is heated once every hour. Heating stops ac-
U68 ...
cording to the set value of the return temperature sensor.
U63 ...
The external heat source is blocked. The instantaneous heating
U6B ...
water heater (if installed) is enabled.
U70 ...
&
No frost protection mode via room temperature sensor
U71 ...
&
No room temperature hook-up
U72 ...
&
No room temperature control
U78 ...
U79 ...
U7A ...
Heat pump module diagnosis
Information regarding the diagnosis at the heat pump is displayed in menu item
"Diag. HP module" at the contractor level.
1. "Device settings"
2. "Contractor level" (for "Con-
tractor" access rights see
page 131)
3. "Further menu items"
4. "Diag. HP module" see tables
"Displays" and "Faults at the elec-
tronic expansion valve"
126
(cont.)
5. "ÓT/P" for the last recorded com-
Note
If the heat pump is stopped due to
a fault, the data is retained. Other-
wise the values are overwritten
when the compressor starts again.
pressor temperatures and
pressures, see table
"Further temperatures,
pressures and fault mes-
sages" and "Faults and
messages (Err/Msg)"