Q: Bilge Pump is running, but Bilge Well water level is not reducing. Why?
E/R Bilge System pipe line:
Bilge Well -> Strainer -> Valve -> Bilge Pump suction valve -> Bilge Pump suction strainer -> Bilge Pump -> Bilge Pump discharge valve -> Bilge Primary Tank.
Fluid (air/liquid) generally flow from higher pressure zone to lower pressure zone. Since Bilge Wells are exposed to the atmosphere (meaning Bilge water is unlike Seawater with positive pressure) and usually about 1.5~2 metres lower in height below the Bilge Pump, the Bilge Pump have to create lower pressure zone on the suction side, like a vacuum cleaner in order to suck the Bilge water towards the Bilge Pump.
Always start troubleshooting from the easiest/most common possibility, and work towards the most uncommon possibility. Please refer to the flow chart I made: