137
Fault mes-
sage
Cause Remedy Re-
set-
ting
"422: State
BUC Eng bu
incon"
Faulty communication be-
tween Stirling burner and
control unit.
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).
AR
"423: State
BUC Supp
bu inco"
Faulty communication be-
tween auxiliary burner and
control unit.
AR
"424: Rep.
loss flame
Eng bu"
Repeated Stirling burner
flame failure.
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.
UR
"425: Rep.
loss of fl'
Supp bu"
Repeated auxiliary burner
flame failure.
UR
"428: Boiler
flow eng
bu"
Minimum flow rate to operate
the Stirling burner not
reached.
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.
AR
"447: BX 6
no function"
Fault in sensor B42/B10:
Plug not inserted correctly.
Check connection (see
page 140)
"457: BX 7
no function"
Internal appliance tempera-
ture sensor faulty.
Check sensor and connect-
ing cable (see page 145).
Troubleshooting
Fault messages
(cont.)
5618 294 GB
Service
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