6 720 820 872 (2016/12)
CR 400 | CW 400 | CW 800
Troubleshooting | 49
Fault code
Sub-code Cause or fault description
Test procedure / Cause
Action
A01
808
DHW heating: DHW temp.
sensor 1 faulty.
If the DHW function is not
needed, deactivate it in the
user interface
No DHW system installed
Deactivate DHW system in the
service menu
Check connecting lead between control unit
and DHW temperature sensor
If there is a defect, replace the
sensor
Check the electrical connection of the
connecting lead in the control unit
If a screw or plug is loose, rectify
the contact problem
Check the hot water temperature sensor as
shown in table
If values do not match, replace the
sensor
Check the voltage at the terminals of the hot
water temperature sensor in the control unit
according to table
If the sensor values matched, but
the voltage values do not match,
replace the control unit
A01
809
DHW heating: DHW temp.
sensor 2 faulty.
If the DHW function is not
needed, deactivate it in the
user interface
No DHW system installed
Deactivate DHW system in the
service menu
Check connecting lead between control unit
and DHW temperature sensor
If there is a defect, replace the
sensor
Check the electrical connection of the
connecting lead in the control unit
If a screw or plug is loose, rectify
the contact problem
Check the hot water temperature sensor as
shown in table
If values do not match, replace the
sensor
Check the voltage at the terminals of the hot
water temperature sensor in the control unit
according to table
If the sensor values matched, but
the voltage values do not match,
replace the control unit
A01
810
Domestic hot water remains
cold
Check if water is possibly being drawn from
the DHW cylinder constantly due to a leak or
taps being open
If water is being drawn constantly,
take action to stop this
Check the position of the hot water
temperature sensor; it may be attached
incorrectly or suspended in the air
Position the hot water temperature
sensor correctly
If the DHW priority was deselected and
heating and DHW are running in parallel, the
boiler output may not be sufficient
Set DHW heating to "priority"
Check whether the heating coil in the cylinder
has been vented completely
Vent if necessary
Check the connection pipes between the heat
source (boiler) and cylinder, and with the aid
of the installation instructions, ensure they
are connected properly
Rectify any faults in the pipework
Using the technical documentation, check
whether the installed cylinder primary pump
can deliver the required output
Replace the pump if there are
deviations
Excessive losses in the DHW circulation line
Check DHW circulation line
Check the hot water temperature sensor
according to table
Replace the sensor if there are
deviations from the table values
Table 25 Fault displays
Summary of Contents for CR 400
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