133
Dis-
played
fault
code
Const.
Weath.-
comp.
System char-
acteristics
Cause
Measures
F3
X
X
Burner in a fault
state
Flame signal
is already
present at
burner start
Check ionisation
electrode and con-
necting cable.
Press reset button
R
.
F6
X
X
Burner in a fault
state
Boiler water
temperature
sensor tem-
perature val-
ues vary too
widely from
one another
Replace boiler wa-
ter temperature
sensors.
F8
X
X
Burner in a fault
state
Fuel valve
closes too
late
Check gas train.
Check both control
paths.
Press reset button
R
.
F9
X
X
Burner in a fault
state
Fan speed
too low during
burner start
Check fan, fan con-
necting cables and
power supply;
check fan control.
Press reset button
R
.
FA
X
X
Burner in a fault
state
Fan not at
standstill
Check fan, fan con-
necting cables and
fan control.
Press reset button
R
.
FC
X
X
Burner in a fault
state
Gas train faul-
ty, faulty mod-
ulation valve
control or flue
gas path
blocked
Check gas train.
Check flue sys-
tem.
Press reset button
R
.
Troubleshooting
Fault codes
(cont.)
5623 520 GB
Service