Operating and fault displays
57
Condens 7000 FP – 6721846699 (2022/12)
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 the fan if necessary.
V 3C 538 Fan speed too
slow.
The actual speed
detected is slower than
the set speed.
Dirt in fan.
Defective fan.
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 a value of
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"
( Chapter 12,
page 52)
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.
An 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)
Fault
code
Sub
code
Cause Description Test procedure/Cause Action
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