Viessmann VITOCAL 300-G Installation And Service Instructions Manual page 144

Troubleshooting
Messages
(cont.)
Message
System characteristics Cause
CE KM BUS ext. extension
CF Communication module
144
Communication error -
KM BUS external exten-
sion H1
Communication error -
LON module in control
unit
Measures
Check external exten-
sion H1 connections and
connecting cables.
Check connections at the
controller and sensor
PCB, plug aVG KM BUS.
A fluctuating DC voltage
between approx. 20 V and
30 V can be measured at
the terminals.
Check LON communica-
tion module and replace if
required.
If required, replace in the
following order:
■ Control and sensor
PCB
■ Ribbon cables between
controller and sensor
PCB and main PCB
■ Main PCB