Grundfos Unilift AP35B Installation And Operating Instructions Manual page 14

Fault
4. The pump runs
but delivers no
flow.
14
Cause
a) The pump is blocked by
impurities.
b) The outlet pipe or the non-return
valve is blocked by impurities.
c) The impeller is not properly
fixed to the shaft.
d) Air is trapped in the pump.
e) The liquid level is too low. The
pump inlet is not completely
submerged in the pumped
liquid.
f) The float switch does not move
freely.
Remedy
Clean the pump. See section
8.1 Cleaning the pump.
Clean the outlet pipe or the non-
return valve.
Tighten the impeller.
Vent the pump and the outlet pipe.
Submerge the pump inlet in the
liquid or adjust the float switch.
Make the float switch move freely.