Viessmann Vitocrossal CRU 800 Service Instructions For Contractors page 41

Fault codes with display on burner control unit
Displayed fault System characteristics
code
F F4 Poor start-up characteristics
(start enrichment). Solenoid
valve not switching.
F F4 Flame does not build during
the safety time, no signal re-
ported by the ionisation flame
monitor.
F F4 Flame does not build during
the safety time, no signal re-
ported by the ionisation flame
monitor.
F F4 Flame does not build during
the safety time, no signal re-
ported by the ionisation flame
monitor.
F F5 Air pressure switch 1 reports
no air pressure, fan not run-
ning.
F F5 Air pressure switch 1
switches off during operation.
F F6 Gas pressure switch reports
no gas pressure.
F F7 Fan pressure is created dur-
ing the idle state check of air
pressure switch 1.
F F7 Contact of air pressure switch
1 not in idle state
F F8 Flame tears off during opera-
tion.
F F8 Flame tears off during opera-
tion.
F F8 Flame tears off during opera-
tion.
F F8 Flame tears off during modu-
lation (burner output increa-
ses).
F F9 Fan not running; fan speed
not reached.
F F9 Status duration too long, fan
ramp-up
F F9 Fan speed deviation
(cont.)
Cause
Compensation lines not
connected, solenoid valve
faulty, output relay of
burner control unit faulty
Incorrect gas type selec-
ted
Gas train does not open.
Combustion characteris-
tics not ideal
Air pressure switch 1 faul-
ty, incorrectly connected
or incorrectly set
Flue gas back pressure,
condensate banked up, air
pressure switch 1 hose
faulty, connecting hose
leaking
Gas shut-off valve closed;
gas pressure switch faulty;
multiple problems with gas
supply
Wind influence on fan
Air pressure switch 1 faul-
ty
Incorrect gas type selec-
ted
Burner gauze assembly
faulty
Combustion characteris-
tics not ideal
Combustion characteris-
tics not ideal
Air pressure switch adjus-
ted incorrectly.
Fan faulty; cables are faul-
ty or broken
Internal fault; fan cannot
reach its set value.
Fan faulty, cable " a-Ö A"
faulty or broken
Troubleshooting
Measures
Check compensation lines and
connections, replace compensa-
tion lines. Replace the solenoid
valve. Replace burner control unit.
Adjust gas type (see page 11).
Check connecting cable. Check
the gas train and replace if re-
quired.
Adjust burner setting. If necessary
also adjust the setting screws
when the burner is off to facilitate
the burner start.
Replace air pressure switch 1, con-
nect or adjust correctly.
Remove flue gas back pressure.
Check for backed up condensate.
Reset the burner control unit. Re-
place hose.
Open the gas shut-off valve. Check
gas flow pressure. Replace gas fil-
ter if required. Reset the burner
control unit. Replace gas train.
Check the flue draught (chimney).
Replace air pressure switch 1.
Adjust gas type (see page 11).
Check the burner gauze assembly.
Replace the burner gauze assem-
bly if it is damaged.
Adjust burner (see from page 16).
Adjust burner (see page 16).
Adjust air pressure switch (see
page 57).
Check cables. Replace fan if re-
quired.
Replace fan or burner control unit.
Check cable. Replace cable
" A" or fan if necessary.
a-Ö
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