Viessmann Vitodens 333 Service Instructions Manual page 81

Checking and acknowledging faults
Display Const.
fault code
F3 X
F4 X
F7 X
F8 X
F9 X
Weat- System
h. character-
comp. istics
X Burner in
fault state
X Burner in
fault state
X Burner
blocked
X Burner in
fault state
X Burner in
fault state
Troubleshooting
(cont.)
Cause Remedy
Flame signal is al- Check ionisa-
ready present at tion electrode
burner start and leads.
Press E.
No flame signal is Check ionisa-
present tion electrode
and leads,
measure ioni-
sation cur-
rent, check
gas pressure,
check gas
combination
valve, igni-
tion, ignition
module, igni-
tion electro-
des and
condensate
drain.
Press E.
Differential pres- Check differ-
sure sensor faulty ential 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 fan,
at burner start check fan
cables and
supply, check
fan control.
Press E.
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