Operating and fault displays
47
Condens 7000 F – 6720871560 (2019/11)
V
3C
537 No speed signal.
There is no speed feedback
message at the burner
control unit, although the
fan should be in operation.
Check the connecting leads between
the burner control unit and the fan
for faulty contacts, breaks and
damage.
Check the plug-in connectors at the
burner control unit and fan.
▶ Establish good electrical contact.
Replace cables if necessary.
▶ Replace the burner control unit.
▶ Replace fan if necessary.
V
3C
538 Fan speed too
slow.
The actual speed detected
is slower than the set
speed.
Dirt in fan.
Fan defective.
▶ Clean the fan if necessary.
▶ Replace fan.
V
3C
540 Fan speed too
fast.
The actual speed detected
is faster than the set
speed.
Flue resistance too high
(>150 Pa).
Check PWM signal/burner control
unit connecting cable for faulty
contacts, breaks or damage.
Check plug-in connectors for
damage.
Check flue resistance.
▶ Establish good electrical contact.
Replace cables if necessary.
▶ Replace the burner control unit.
▶ Install butterfly valve/secondary air
device, if necessary.
V
4A
520 Intelligent high
limit safety cut-out
(ISTB) for the flow
The flow temperature has
reached 110 °C.
Since the temperature increase in
the boiler is monitored by the boiler
water temperature sensor, and
consequently the burner is switched
off in good time, this fault display can
not appear under normal
circumstances.
Unfavourable hydraulics in two-
boiler systems: the boilers influence
each other reciprocally, e.g. via the
return or flow.
▶ Check hydraulics.
V
4A
575 ISTB (intelligent
high limit safety
cut-out)
responds.
The boiler flow
temperature has reached
its maximum permissible
level.
High limit safety cut-out has
triggered.
▶ Check the air/gas ratio control valve.
(Does the flame extinguish after a
controlled shutdown?)
V
4A
700
Factory supplied condition Boiler is locked out
▶ Reset the boiler with "Reset"
(
V
4U
521 Sensor differential
on the boiler
temperature
sensor between
temperature
sensors 1 and 2 is
too high.
Temperature differential
between temperature
sensors 1 and 2 is too high
(deviation > 5 K/2s).
Check whether the reset button on
the burner control unit lights up.
Check whether the plug-in
connectors at the boiler temperature
sensor and the burner control unit
are dirty or damaged.
Check the pressure drop values at
boiler temperature sensor against
the table and visually check the plug
on the temperature sensor.
Check the connecting lead for
continuity.
▶ Press the reset button on the burner
control unit.
▶ If required, clean or replace the plug-
in connectors.
▶ If sensor values deviate from those
specified or the plug is faulty, replace
the boiler water temperature sensor.
▶ If there are any deviations, replace
the connecting lead.
V
4U
522 Short circuit
between
temperature
sensors 1 and 2 at
the boiler water
temperature
sensor.
A temperature sensor fault
was detected in test mode.
Check sensor lead.
Check plug-in connector.
Check sensor readings against table.
Check the voltage values at the
sensor against the table.
▶ Replace if damaged.
▶ Clean if dirty or replace if necessary.
▶ Reconnect any loose plugs.
▶ Replace the temperature sensor, if
there are any deviations from the
table.
V
4U
524 Short circuit at the
boiler water
temperature
sensor.
Excessively high
temperature (> 130 °C) is
measured at the boiler
water temperature sensor.
Check sensor lead.
Check plug-in connector.
Check sensor readings against table.
Check the voltage values at the
sensor against the table.
▶ Replace if damaged.
▶ Clean if dirty or replace if necessary.
▶ Reconnect any loose plugs.
▶ Replace the temperature sensor, if
there are any deviations from the
table.
Type
1)
Error
code
Sub-
code
Cause
Description
Test procedure/Cause
Action