If you have this problem, there are several possibilities. If the pump is running but the water is not being pumped out, it could be that the pump's impeller has jammed or the pump is clogged. This often happens with waste water pumps for water containing faeces.
It is also possible that an installation part inside the wastewater pump has broken off and the impeller no longer turns. Another possibility is that the non-return valve does not open. This can be the result of the non-return valve not having been maintained or the pump not having been in use for a long time, which has caused it to become stuck.