Grundfos NB Series - 3 Fault Finding

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3. Fault finding
Warning
Before removing the terminal box cover and before any dismantling of the pump, make sure
that the electricity supply has been switched off. It must be ensured that it cannot be
accidentally switched on.
Fault Cause Remedy
1. The pump delivers no
or too little liquid.
a) Wrong electrical connection (2 phases). Check the electrical connection, and remedy, if
necessary.
b) Wrong direction of rotation. Interchange two phases of the mains supply.
c) Air in suction pipe. Vent the suction pipe or the pump, and replenish.
d) Counter-pressure too high. Set the duty point in accordance with the data
sheet. Check the system for impurities.
e) Inlet pressure too low. Increase the liquid level on the suction side.
Open the isolating valve in the suction pipe.
See the installation and operating instructions.
f) Suction pipe blocked, or impurities in
impeller.
Clean the pump.
g) Pump draws in air due to defective seal. Check the pipeline seals, pump housing gaskets
and shaft seals, and replace, if necessary.
h) Pump draws in air due to low liquid level. Increase the liquid level on the suction side, and
keep it as constant as possible.
2. The motor-protective
circuit breaker has
tripped because the
motor is overloaded.
a) Pump blocked by impurities. Clean the pump.
b) Pump running above the rated duty point. Set the duty point in accordance with the data
sheet.
c) Density or viscosity of the liquid is higher
than specified when ordering.
If less flow is sufficient, reduce the flow on the
discharge side. Or fit a more powerful motor.
d) Motor starter overload setting is incorrect. Check the setting of the motor-protective circuit
breaker, and replace, if necessary.
e) The motor runs on two phases. Check the electrical connection. Replace the fuse,
if defective.
3. Pump makes too
much noise.
Pump runs unevenly
and vibrates.
a) Inlet pressure too low (cavitation). Increase the liquid level on the suction side.
Open the isolating valve in the suction pipe.
See the installation and operating instructions.
b) Air in suction pipe or pump. Vent the suction pipe or the pump, and replenish.
c) Counter-pressure is lower than specified. Set the duty point in accordance with the data
sheet.
d) Pump draws in air due to low liquid level. Increase the liquid level on the suction side, and
keep it as constant as possible.
e) Impeller out of balance (clogged impeller
blades).
Clean and check the impeller.
f) Inner parts worn. Replace defective parts.
g) Pump stressed by the pipework
(thus causing starting noise).
Mount the pump so that it is not stressed.
Support the pipes.
h) Defective bearings. Replace the bearings.
i) Defective motor fan. Replace the fan.
j) Foreign bodies in the pump. Clean the pump.
k) Frequency converter operation. See the installation and operating instructions.
4. Leakage in pump or at
connections.
Leakage in
mechanical shaft seal.
a) Pump stressed by the pipework
(thus causing leaks in the pump or at
connections).
Mount the pump so that it is not stressed.
Support the pipes.
b) Pump housing gaskets and gaskets at
connections defective.
Replace pump housing gaskets or gaskets at
connections.
c) Mechanical shaft seal dirty or stuck
together.
Check and clean the mechanical shaft seal.
d) Mechanical shaft seal defective. Replace the mechanical shaft seal.
e) Shaft surface defective. Replace the shaft.