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Troubleshooting
Fault messages
(cont.)
Displayed fault
System characteristics
code
F.69
Burner in a fault state
F.70
Burner in a fault state
F.71
Burner in a fault state
F.72
Burner in a fault state
F.73
Burner in a fault state
F.74
Burner locked out.
Internal circulation pump off.
No central heating and no
DHW heating.
F.77
Burner in a fault state
F.89
No central heating and no
DHW heating
F.91
Function of affected exten-
sion in emergency mode
82
Cause
Ionisation current lies out-
side the permissible range
Internal burner control unit
fault
Fan speed too low
Fan idle state not reached Reset the appliance.
Internal communication
error
System pressure too low
Data memory burner con-
trol unit
Internal circulation pump
blocked
DIO electronics module
communication error
Measures
Check ionisation electrode for the
following:
Check whether insulation block is
■
touching electrode ceramic.
Check gas train: Activate "Mini-
■
mum heating output" for ap-
prox. 4 min in actuator test. If this
causes a fault to occur, replace
BCU burner control unit.
In the actuator test, switch from
■
"Minimum heating output" to
"Maximum heating output". If
this fault occurs during modula-
tion, check the intake screen for
contamination. Replace the fan
unit if necessary.
Replace BCU burner control unit:
See page 100.
Check fan for blockage.
■
Check setting for gas type and
■
flue system.
Reset the appliance.
If fault occurs repeatedly, replace
fan unit.
Reset the appliance.
If fault recurs, replace BCU burner
control unit: See page 100.
Top up with water.
Vent the system.
If the fault occurs repeatedly:
Check system pressure sensor
■
with external pressure gauge.
Check diaphragm expansion
■
vessel pre-charge pressure.
Check settings for set system
■
pressure and range.
Reset the appliance.
If fault recurs, replace BCU burner
control unit: See page 100.
Check circulation pump. Replace if
necessary.
Check connections to DIO elec-
tronics module and connection to
heat management unit.
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