Viessmann Vitodens 300 Service Instructions Manual page 83

Checking and acknowledging faults
Displayed Const.
fault code
F4 X
F7 X
F8 X
F9 X
Weat- System
her- character-
comp. istics
X Burner in
fault state
X Burner
blocked
X Burner in
fault state
X Burner in
fault state
Troubleshooting
(cont.)
Cause Remedy
No flame signal is Check the
present ionisation
electrode and
leads, mea-
sure the ioni-
sation cur-
rent, check
the gas pres-
sure, check
the gas com-
bination
valve, igni-
tion, ignition
module, igni-
tion electro-
des and the
condensate
drain.
Press E.
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.
83