Viessmann VITOTRONIC 100 Installation And Service Instructions Manual page 120

Troubleshooting
Faults which are displayed at the programming unit
LON users fault messages
Only if the control unit is the fault manager (code "79:1").
Fault
System
code
characteristics
Control mode
01
to
98
120
Cause
A user fault has
occurred, e.g. 12
(Vitotronic 050)
No connection to
the user
(cont.)
Remedy
Download fault code
to user
Installation
and service
instructions
of the
relevant
control unit
Check coding
(see page 99)
Check connecting
LON cable
Update user list
(see page 99)
Carrying out a
user check
(see page 100)