Based on our experience, we could imagine that there is no technical fault with the pump, but that air is being sucked in on the suction side of the pump (suction hose) or that there is some other defect.
You can easily check yourself whether the pump has such a fault and is therefore not developing any power as follows:
During operation, hold the end of the hose under the surface of the water (in a bucket, for example). If you keep seeing air bubbles, the pump has a fault in the suction line area.
Possible causes are
1. the suction side is not vacuum-tight. The suction side must be completely airtight, not just watertight.
2. the suction filter is heavily soiled. The suction filter must be clean.
3. the non-return valve in the suction hose is stiff. The non-return valve must not be jammed.
Ensure that only suitable hoses or connectors are used on the suction side. Pressure hoses can contract after a certain time and thus prevent the flow of water.
When using a claw coupling on the suction side, make sure that a claw coupling suitable for the suction side is used.