Viessmann Vitocal 350-A Installation And Service Instructions Manual page 136

Troubleshooting
Control unit diagnostics
Message
System characteristics Cause
«3A Evaporator sensor
«3B Hot gas
«40 Flow sensor HC2
Mixer heating circuit M2
is closed
«41 Flow sensor HC3
Mixer heating circuit M3
is closed
«43 Flow sensor system
«48 Flow sensor HC2
Mixer heating circuit M2
is closed
«49 Flow sensor HC3
Mixer heating circuit M3
is closed
136
(cont.)
Break - evaporator tem-
perature sensor
Break - hot gas tempera-
ture sensor
Short circuit, flow tem-
perature sensor in heat-
ing circuit with mixer M2
Short circuit, flow tem-
perature sensor in heat-
ing circuit with mixer M3
Short circuit, system flow
temperature sensor
(downstream of heating
water buffer cylinder)
Lead break, flow temper-
ature sensor in heating
circuit with mixer M2
Break, flow temperature
sensor heating circuit
M3
Measures
Check pressure drop
value (type Pt 500) at con-
nections 3X1.5 and
3X2.5; replace sensor if
required.
Check pressure drop
value (type Pt 500) at con-
nections 3X1.1 and
3X2.1; replace sensor if
required.
Check resistance (Ni 500)
at connections 3X1.10
and 3X2.10; replace sen-
sor if required.
Check resistance (Ni 500)
at extension kit connec-
tions for heating circuit
with mixer; replace sensor
if required.
Check resistance (Pt 500)
at connections 3X1.9 and
3X2.9; replace sensor if
required.
Check resistance (Ni 500)
at connections 3X1.10
and 3X2.10; replace sen-
sor if required.
Check resistance (Ni 500)
at extension kit connec-
tions for heating circuit
with mixer; replace sensor
if required.