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121
Dis-
played
fault
code
Const.
Weath.-
comp.
System char-
acteristics
Cause
Measures
A4
X
Control mode
Max. system
pressure ex-
ceeded
Check system
pressure max.
3 bar (0.3 MPa)
Check the function
and sizing of the di-
aphragm expan-
sion vessel.
Vent the heating
system.
A7
X
Control mode
as per deliv-
ered condition
Programming
unit faulty
Replacing pro-
gramming unit
b0
X
X
Burner blocked Short circuit,
flue gas tem-
perature sen-
sor
Check flue gas
temperature sen-
sor
b1
X
X
Control mode
as per deliv-
ered condition
Communica-
tion error,
programming
unit
Check connections
and replace pro-
gramming unit if re-
quired
b5
X
X
Control mode
as per deliv-
ered condition
Internal error
Replacing the con-
trol unit
b7
X
X
Burner blocked Coding card
fault
Plug in coding card
or replace if faulty
b8
X
X
Burner blocked Lead break,
flue gas tem-
perature sen-
sor
Check flue gas
temperature sen-
sor
bA
X
Mixer regulates
to 20 °C flow
temperature.
Communica-
tion error, ex-
tension kit for
heating circuit
2 (with mixer)
Check extension
kit connections and
code.
Troubleshooting
Fault codes
(cont.)
5585 174 GB
Service