Viessmann Vitopend 100-W Installation And Service Instructions For Contractors page 37

Function sequence and possible faults
Control unit issues
a heat demand
Yes
Ignition
Yes
Gas train opens
Yes
Ionisation current
builds (higher than
2 µA)
Symbol A
Yes
Burner in opera-
tion
Display
No
No Fault "F4"
No
Fault "F4"
No Fault "F4"
No Shuts down below
the set boiler water
temperature and
restarts immediate-
ly
Troubleshooting
Action
Increase set value
and ensure heat is
drawn off
Check the ignition
module connec-
tion
Check the gas
train (control volt-
age 230 V) and
gas supply pres-
sure
Check the ionisa-
tion current, check
the electrode ad-
justment and the
gas line for air-
locks.
Check the flue sys-
tem for tightness
(flue gas recircula-
tion); check the
gas flow pressure
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