Viessmann MPA51 Operating And Service Instructions page 20

Diagnosis
Diagnosis
(cont.)
Fault Display
*1
code
F 42 F 42
F 43 F 43
F 50 F 50
F 53 9
All fault codes are saved to the fault memory and the last 10 can be called up.
*1
20
System charac-
teristics
No fan feedback
Burner control unit
in fault state
Burner control unit
in fault state
Gas shortage at
gas pressure
switch; check
valve tightness
Cause
Fan faulty; exter-
nal power supply
to fan not connec-
ted or faulty; cable
"100A" faulty or
broken; fan
blocked (e.g. by a
foreign body)
Internal fault of the
burner control unit
and during test of
ionisation input
Internal fault in
servomotor feed-
back; output relay
does not respond
Gas valve does
not open; gas
valve leaking
Measures
Check cable
"100A"; check ex-
ternal power sup-
ply; replace cable
or fan; remove for-
eign body
Replace burner
control unit
Replace burner
control unit
Replace gas train.
After replacing the
gas train, extended
reset (see
page 18)