Fault Finding - Grundfos MTB Serie Manual Del Usuario

13. Fault finding

Warning
Before removing the terminal box cover and before any removal/dismantling of the pump,
make sure that the electricity supply has been switched off and that it cannot be accidentally
switched on.
Fault
1. Motor does not run
when started.
2. Motor starter overload
trips out immediately
when supply is
switched on.
3. Motor starter overload
trips out occasionally.
4. Motor starter has not
tripped out but the
pump does not run.
5. Pump capacity not
constant.
6. Pump runs but gives
no liquid.
7. Pump runs backwards
when switched off.
18
Cause
a) Electrical supply failure.
b) Fuses blown.
c) Motor starter overload has tripped
out.
d) Main contacts in motor starter are
not making contact or the coil is
faulty.
e) Impeller blocked. The motor cannot
rotate.
f) Control circuit fuses are defective.
g) Motor is defective.
a) One fuse is blown.
b) Contacts in motor starter overload
are faulty.
c) Cable connection is loose or faulty.
d) Motor winding is defective.
e) Pump mechanically blocked.
f) Overload setting too low.
a) Overload setting too low.
b) Supply voltage periodically too low
or too high.
c) Differential pressure across pump
too low.
a) Check 1 a), b), d) and e).
a) Pump inlet pressure is too low.
b) Suction pipe/pump partly blocked by
impurities.
c) Pump draws in air:
- Leakage in pipe
- Water level in tank too low.
a) Suction pipe/pump blocked by
impurities.
b) Foot or non-return valve blocked in
closed position.
c) Leakage in suction pipe.
d) Air in suction pipe or pump.
e) Motor rotates in the wrong direction. Change the direction of rotation.
a) Leakage in suction pipe.
b) Foot or non-return valve defective.
c) Foot or non-return valve blocked in
open or partly open position.
Remedy
Connect the electricity supply.
Replace the fuses.
Reactivate the motor starter.
Replace the contacts or magnetic coil.
Clean the inside of the pump and
inspect for damages.
Repair the control circuit.
Replace the motor.
Replace the fuse.
Replace the motor starter contacts.
Fasten or replace the cable.
Replace the motor.
Remove the blocking.
Set the motor starter correctly.
Set the motor starter correctly.
Check the supply voltage.
Vent the pump. See section
8.3 Starting.
Increase the inlet pressure.
Clean the pipe/pump.
- Repair the leakage.
- Increase the water level in the tank.
Vent the system.
Clean the pipe/pump.
Clean/repair the foot or non-return
valve.
Repair the leakage.
Vent the pump.
Repair the leakage.
Replace the defective foot or non-
return valve.
Clean/repair the foot or non-return
valve.