Viessmann VITODENS 111-W Installation And Service Instructions Manual page 91

Fault messages
(cont.)
Displayed fault System characteristics
code
981 No DHW heating
982 No central heating, no DHW
heating
Status messages
The following messages can be displayed using the
"ViGuide" software tool:
Message on the display
S.9
S.29
S.36
S.60
S.74
S.75
S.94
S.95
S.96
S.154
Cause
Minimum system pressure
is too low during DHW
heating. Possible causes:
Shut-off valve
■
Too restricted
■
Limescale build-up
■
Sludge
■
Incorrect hydraulic con-
■
figuration
Circulation pump faulty
■
Air in heating circuit
■
System pressure unsta-
■
ble or too low
Circulation pump heating
circuit 1 running dry.
Meaning
Fan pre-purge for heating mode
Standard mode for heating
Comfort mode for DHW draw-off
Summer mode active (outside temperature economy function)
Heating suppression, heating
DHW circulation pump active
No demand, external hook-up, heating circuit 1
No demand, external hook-up, heating circuit 2
No demand, external hook-up, heating circuit 3
Due to insufficient heat transfer in heating system, burner operation not required
Troubleshooting
Measures
Check that the cylinder flow and
■
return are open.
Ensure that all quick-action air
■
vent valves on the appliance side
are permanently open.
Run the entire venting program
■
of the heating circuit again (se-
lect via service menu). Important:
The quick-action air vent valve in
the boiler circuit must be perma-
nently open!
Check the set hydraulic scheme
■
and correct if necessary.
Check the size and pre-charge
■
pressure of the external dia-
phragm expansion vessel.
Check the set system pressure
■
(this fault is more likely if the sys-
tem pressure is too low).
Check the quick-action air vent
■
valves for leaks and replace if
necessary.
Check the circulation pump and
■
replace if necessary.
The pause time for DHW heating
■
can be terminated by a mains re-
set of the HMU heat manage-
ment unit. Switch the appliance
off and on again at the appliance
switch.
Check the DEV; check the circula-
tion pump.
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