1.      Pump is not primed. The water pump pouring through the primer button, the exhaust button must be opened until the water in the pump overflows of the primer.
2.     The pump runs in the opposite direction to the design.
3.     The valve is closed, or blocked in the suction or discharge hose. Check the flange gasket that must be cut through in its center.
4.     The mouth of the straw is not submerged in the suction tank. You can increase the length of the suction pipe or increase the water surface.
5.     Foot valve is closed or clogged.
6.     Filter grid clogged
7.     Suction pressure too low.
8.    Suction brach valve is open
9.     Suction pipe is not tight
10.  The system operates under negative pressure. Sleeve seals are permitting air to enter the system. You should change the sealing type by mechanical seals.
11.   The pump was worn out. Allowable clearance has been increased excessively.
12.   There are broken parts. Check pump shaft, coupling, internal components.
13.   No electric supplying