Viessmann VITOCAL 300-G Installation And Service Instructions Manual page 134

Troubleshooting
Messages
(cont.)
Message
System characteristics Cause
6B Ext. heat source
External heat source is
blocked. Instantaneous
heating water heater (if
installed) is enabled
70 Room sensor HC1
■ No frost protection
mode via room temper-
ature sensor
■ No room temperature
hook-up
■ No room temperature
control
71 Room sensor HC2
■ No frost protection
mode via room temper-
ature sensor
■ No room temperature
hook-up
■ No room temperature
control
72 Room sensor HC3
■ No frost protection
mode via room temper-
ature sensor
■ No room temperature
hook-up
■ No room temperature
control
73 Room sensor SKK
134
Lead break, external
heat source temperature
sensor
Short circuit, room tem-
perature sensor heating
circuit A1
Short circuit, room tem-
perature sensor heating
circuit M2
Short circuit, room tem-
perature sensor heating
circuit M3
Short circuit, room tem-
perature sensor, cooling
circuit
Measures
Check pressure drop
value (Pt 500) at plug-in
connection F20 and termi-
nals X6.8/X6.9; replace
sensor if required.
Check remote control
sensor and replace if
required (see Vitotrol
service instructions).
Check remote control
sensor and replace if
required (see Vitotrol
service instructions).
Check remote control
sensor and replace if
required (see Vitotrol
service instructions).
Check resistance (type Ni
500) at plug-in connection
F16; replace sensor if
required.