Viessmann VITODENS 100-W Installation And Service Instructions Manual page 41

Fault messages on the display
Displayed System characteris-
fault code tics
F4 Burner in a fault
state
F8 Burner in a fault
state
F9 Burner in a fault
state
FA Burner in a fault
state
FC Burner blocked
(cont.)
Cause
No flame signal
detected
Fuel valve closes
too late
Fan speed too low
during burner start
Fan not at stand-
still
Electrical fan con-
trol (control unit)
faulty
Troubleshooting
Measures
Check the ionisation elec-
trode and cables, check
the gas pressure, check
the gas train, ignition, igni-
tion module and conden-
sate drain.
Press "Reset" (see
page 42).
Check gas train. Check
both control paths.
Press "Reset" (see
page 42).
Check fan, fan connecting
cables and power supply;
check fan control.
Press "Reset" (see
page 42).
Check fan, fan connecting
cables and fan control.
Press "Reset" (see
page 42).
Check fan connecting
cable; if required, replace
or replace control unit
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