H Faults With Fault Display - Viessmann Vitocrossal 300 Service Instructions Manual

Diagnostics
(cont.)
Faults with fault display
General process error
Fault System
code characteristics
display
20 The fan does not
stop during the air
pressure switch idle
state check
Air pressure switch
contact does not
open (fan idle)
21 Fan runs, air
p pressure switch does
not signal air
pressure
Fan does not run
22 Burner does not start Jumper B 3 contact at
Only if a gas
governor was
retrofitted:
Gas governor does
not signal gas
pressure
Cause
Wind influence on
fan
Air pressure switch
faulty
Air pressure switch
faulty
Air pressure switch
connection leaks
(sealing washers
faulty)
Excessive pressure
drop on flue gas side
Fan faulty, cables
faulty or broken
slot aYA broken
(missing or faulty)
Gas shut−off valve
closed, gas governor
faulty
Troubleshooting
Remedy
Check flue gas
draught (chimney)
Replace air pressure
switch
Replace air pressure
switch
Check sealing
washers and replace
if necessary
Remove any
condensate and
clean flue gas system
if required
Check cables and
replace fan, if
required
Check strapping
plug and replace if
required
Open gas shut−off
valve, check gas
supply pressure and
clean gas filter, if
necessary
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