Viessmann VITODENS 333 Service Instructions Manual page 82

Troubleshooting
Checking and acknowledging faults
Fault code Const.
in the dis-
play
F7 X
F8 X
F9 X
FA X
Fd X
82
Weat- System
h. character-
comp. istics
X Burner
blocked
X Burner in
fault state
X Burner in
fault state
X Burner in
fault state
X Burner
blocked
(cont.)
Cause Remedy
Differential pres- Check the dif-
sure sensor faulty ferential pres-
sure sensor
and lead.
Fuel valve closes Check gas
too late combination
valve. Check
both control
paths.
Press E.
Fan speed too low Check the
at burner start fan, check the
fan cables
and supply,
check the fan
control.
Press E.
.
Fan speed too high Check the
at burner start fan, check the
fan cables,
check the fan
control.
Press E.
Burner control unit Check the
fault ignition elec-
trodes and
leads. Check
whether a
strong inter-
ference
(EMC) field
exists near
the equip-
ment.
Press E.
If the fault is
not removed,
replace the
control unit.