Troubleshooting - Grundfos CU 321 Installation And Operating Instructions

5.1 Troubleshooting

WARNING!
Before working on the input or output of the CU 321, make sure that the electricity supply has been
switched off and that it cannot be accidentally switched on.
Fault Cause
One fuse in the installation is blown/
tripped out.
Faulty electricity supply.
No light in the
display.
The current-operated or voltage-operated
circuit breaker has tripped out.
The CU 321 may be defective.
If the display is flashing, the pump is
stopped, either due to a stop command
from the
or due to the fact that no water is required
(flashing PSI XXX). XXX indicates the
The pump is not pressure setting in psi.
running.
No connection between the CU 321 and
the pump.
The sensor is defective.
Incorrect pressure in diaphragm tank.
The pump is not of the correct type.
The pressure is
The pressure sensor is positioned too far
not constant.
away from the tap.
The max. speed has been set too low.
The flow is below 10% of max. rated flow
of the pump and the CU 321 operates in
pressure switch mode.
The pump may be defective.
The pump cannot deliver the set pres-
sure.
The pump is
running continu- The pressure sensor is defective.
ously.
The CU 321 is defective.
Off/ button (flashing OFF XXX)
Reset
Remedy
Replace/cut in the fuse.
Check that the electricity supply falls within
the specified range.
Check that the electricity supply corresponds
to the specified voltage range.
Cut in the circuit breaker.
Check that the electricity supply falls within
the specified range.
Replace the CU 321 or call GRUNDFOS
SERVICE for assistance.
Check that the pressure is below the pressure
setpoint.
Check the connection between the CU 321
and the pump.
Restore the connection.
Check the sensor, see the table in section
7. Pressure sensor voltage chart.
Restore the correct pressure in the diaphragm
tank.
If the pump is running and the pressure is
dropping, the pump may be undersized. Or if
the pump is oversized, cycling may occur. See
section 1.4 System sizing. Replace the pump,
if necessary.
Reposition the pressure sensor, see section
1.5 Positioning the pressure sensor.
Review max. speed setting.
Check the pump.
Lower the pressure setting; note that it takes
about 15 to 25 seconds before the pump
stops.
Check that the pressure port of the sensor is
not blocked. If so, remove the blockage.
Try to stop the pump by pressing the
ton. If that is not possible, the CU 321 is defec-
tive.
Off/ but-
Reset
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