Bosch CR 400 Installation Instructions For Contractors page 49

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