Bosch Condens 7000 FP Installation And Service Instructions Manual page 57

1)
Type Fault Sub Cause
code code
V 3C 537 No speed signal.
V 3C 538 Fan speed too
slow.
V 3C 540 Fan speed too
fast.
V 4A 520 Intelligent high
limit safety cut-out
(ISTB) for the flow
V 4A 575 ISTB (intelligent
high limit safety
cut-out)
responds.
V 4A 700
V 4U 521 Sensor differential
on the boiler
temperature
sensor between
temperature
sensors 1 and 2 is
too high.
V 4U 522 Short circuit
between
temperature
sensors 1 and 2 at
the boiler water
temperature
sensor.
V 4U 524 Short circuit at the
boiler water
temperature
sensor.
Condens 7000 FP – 6721846699 (2022/12)
Description Test procedure/Cause
There is no speed Check the connecting leads between
feedback message at the burner control unit and the fan
the burner control unit, for faulty contacts, breaks and
although the fan should damage.
be in operation.
Check the plug-in connectors at the
burner control unit and fan.
The actual speed Dirt in fan.
detected is slower than
Defective fan.
the set speed.
The actual speed Check PWM signal/burner control
detected is faster than unit connecting cable for faulty
the set speed. contacts, breaks or damage.
Flue resistance too high Check plug-in connectors for
(>150 Pa). damage.
Check flue resistance.
The flow temperature Since the temperature increase in
has reached a value of the boiler is monitored by the boiler
110 °C. 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.
The boiler flow High limit safety cut-out has
temperature has triggered.
reached its maximum
permissible level.
Factory supplied Boiler is locked out
condition
Temperature Check whether the reset button on
differential between the burner control unit lights up.
temperature sensors 1
Check whether the plug-in
and 2 is too high
connectors at the boiler temperature
(deviation > 5 K/2s).
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.
A temperature sensor Check sensor lead.
fault was detected in
Check plug-in connector.
test mode.
Check sensor readings against table.
Check the voltage values at the
sensor against the table.
An excessively high Check sensor lead.
temperature (> 130 °C)
Check plug-in connector.
is measured at the
boiler water
Check sensor readings against table.
temperature sensor.
Check the voltage values at the
sensor against the table.
Operating and fault displays
Action
▶ Establish good electrical contact.
Replace cables if necessary.
▶ Replace the burner control unit.
▶ Replace the fan if necessary.
▶ Clean the fan if necessary.
▶ Replace fan.
▶ Establish good electrical contact.
Replace cables if necessary.
▶ Replace the burner control unit.
▶ Install butterfly valve/secondary
air device, if necessary.
▶ Check hydraulics.
▶ Check the air/gas ratio control
valve.
(Does the flame extinguish after a
controlled shutdown?)
▶ Reset the boiler with "Reset"
( Chapter 12,
page 52)
▶ 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.
▶ 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.
▶ 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.
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