Viessmann Vitopend 100-W Installation And Service Instructions Manual page 68

Diagnostics
Function sequence and possible faults
Control unit is-
sues a heat de-
mand
Yes
Fan starts
Yes
Ignition
Yes
Gas train opens
Yes
Ionisation current
builds (above
2 µA)
Symbol A
68
Display
No
No
After approx. 51 s
fault "F05"
No Fault "F04"
No
Fault "F04"
No
Fault "F04"
Measure
Increase set value
and ensure heat is
drawn off
Check the air
pressure switch,
fan, fan connect-
ing cables and fan
power supply
Check the ignition
module connec-
tion
Check the gas
train (230 V con-
trol voltage) and
gas supply pres-
sure
Check the ionisa-
tion current, check
the electrode ad-
justment and the
gas line for air-
locks.