Viessmann Vitotwin 300-W Installation And Service Instructions For Contractors page 137

Fault messages
Fault mes- Cause
sage
"422: State Faulty communication be-
BUC Eng bu tween Stirling burner and
incon" control unit.
"423: State Faulty communication be-
BUC Supp tween auxiliary burner and
bu inco" control unit.
"424: Rep. Repeated Stirling burner
loss flame flame failure.
Eng bu"
"425: Rep. Repeated auxiliary burner
loss of fl' flame failure.
Supp bu"
"428: Boiler Minimum flow rate to operate
flow eng the Stirling burner not
bu" reached.
"447: BX 6 Fault in sensor B42/B10:
no function" Plug not inserted correctly.
"457: BX 7 Internal appliance tempera-
no function" ture sensor faulty.
(cont.)
Remedy
Check the cable to the gas
valve and replace gas valve
if necessary. If the fault has
not been rectified, replace
the control unit PCB (see
page 138).
Check the gas supply. Check
gas type setting (see
page 66).
Check electrodes (see
page 73).
Check function of gas train
and ignition transformer.
Check balanced flue system.
Ensure that flue gases are
not being recirculated.
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 temperature sensors
and flow sensor.
Check connection (see
page 140)
Check sensor and connect-
ing cable (see page 145).
Troubleshooting
Re-
set-
ting
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