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7.1 Fault finding, negative-head pumps (STN, SSN and STL 2.0 CN)
Before starting work on the pump, make sure that the electricity supply has been switched off and that it cannot be
accidentally switched on.
Fault Possible cause Remedy
1. The pump fails to start. a) The electricity supply is switched off. Switch on the electricity supply.
b) The fuses are blown. Replace the blown fuses. If the new ones blow too, the
electric installation should be checked.
c) The built-in thermal protection has switched
off the motor.
The thermal protection resets automatically within
1to2hours.
d) Isolating valves are closed. Open the isolating valves.
e) Strainers are blocked. Close the service isolating gate valves, clean the
strainers and re-open the service isolating gate valves.
f) Pump installed with non-vertical discharge
ports (flow switches).
The pump must be installed with vertical discharge ports
(flow switches).
g) Dry-running protection operated. Switch off the electricity supply for 10 seconds to reset.
2. The flow from the
shower drops.
a) Blocked strainers. Clean the pump strainers.
3. The pump runs
continuously.
a) A flow demand still exists. Check the installation for leaks.
b) Faulty pressure switch. Check the pressure switch.
c) The float in the flow switch is stuck in the
up (on) position.
Make sure that the flow switch can operate correctly and
there is no debris in the flow switch.
d) Flow switch or reed switch faulty or
incorrectly set.
Adjust or replace as appropriate.
4. The pump pulses. a) The use of other taps in the house may
cause the pump to start momentarily.
Contact your installer.
b) Leaks in the system. Check the system for leaks.
c) Faulty non-return valve. Check the non-return valves and replace, if necessary.
5. Pump stops when there
is a demand.
a) Flow demand below 0.4 l/min. Increase the flow demand.
b) Flow switch or reed switch faulty. Replace the flow switch or reed switch.
6. Pump hunts when
shutting down.
a) Incorrect tank air-pressure setting. Adjust the tank air-pressure setting.
b) Insufficient run-on time. Replace the printed-circuit board (PCB).
7. Pump hunts when
starting up.
a) Flow rate below 0.4 l/min. Increase the flow rate.
b) Flow switch or reed switch faulty or
incorrectly set.
Adjust or replace as appropriate.
8. Noisy pump. a) Vibration through pump mounting surface. Mount the pump on a concrete slab to reduce noise.
9. Hose connection
leaking.
a) Hose connection loose. On STL 2.0 CN pumps, ensure that the hose washers
and strainer washers are fitted. Ensure that the plastic
nuts on the hoses are tight.
On STN and SSN pumps, ensure that the hose
connection is fully inserted to a minimum depth of
33 mm.
Grundfos.bk Page 12 Thursday, April 22, 2010 10:28 AM
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