Viessmann Vitotwin 300-W Installation And Service Instructions For Contractors page 125

Fault messages
Fault mes- Cause
sage
"121: Flow Set flow temperature for
temp HC1" heating circuit 1 not reached
"122: Flow Set flow temperature for
temp HC2" heating circuit 2 not reached
"127: Le- Higher DHW temperature not
gionella reached
temp"
"157: Boiler Temperature limiter in the
flow thermo- safety chain has tripped.
stat"
"158: Con- Level switch has tripped.
densate"
(cont.)
Remedy
Check flow temperature sen-
sor and lead (see page 146).
Check that the flow tempera-
ture sensor is installed cor-
rectly.
Check temperature sensors
(see page 140).
Check the system pressure.
Vent the heating system.
Check whether there is any
throughput (code 8366 in di-
agnostics heat generation)
Check function of 3-way
diverter valve.
Check the system pressure.
Vent the heating system.
Check whether there is any
throughput (code 8366 in di-
agnostics heat generation)
Check function of the circula-
tion pump.
Check function of 3-way
diverter valve.
Check condensate drain,
clean siphon.
Check installation position
and function of the level
switch.
Troubleshooting
Re-
set-
ting
UR
UR
125