123
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.
system pressure
6 bar).
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
Replace program-
ming 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 fault, pro-
gramming
unit
Check connections
and replace pro-
gramming unit if re-
quired.
b5
X
X
Control mode
as per deliv-
ered condition
Internal fault
Replace the control
unit.
b7
X
X
Burner blocked Boiler coding
card faulty
Plug in boiler cod-
ing 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.)
5623 520 GB
Service