Why does my boat's bilge pump stop working?
My 12V automatic bilge pump sometimes clears the bilge, but other times it stays silent with water around it. Occasionally I can hear it running without much coming out of the discharge. What should I check before buying another pump?
Answer
Your bilge pump usually stops working because its strainer is blocked, its float switch sticks, or a poor electrical connection cuts power to the motor. First check whether it is silent, running without moving water, or stopping after a few minutes: each symptom points to a different fault.
Check the inlet and switch
If water is rising, start the manual bilge pump and find the source immediately; ordinary bilge pumps are not designed to control serious flooding. Isolate the pump's electrical supply before putting fingers into the impeller or removing wiring.
Lift the sole boards and inspect the pump inlet or separate suction strainer. Hair, cable ties, sawdust and bits of sealant can soon choke it. Debris often emerges from hidden spaces even on a recently cleaned boat.
- Clean the strainer: remove loose rubbish first, then open the serviceable pump housing or strainer bowl as the instructions allow.
- Check the float: it must move freely without catching against a hose, cable or bilge side.
- Check the water depth: an automatic switch needs enough water to reach its starting level; a shallow puddle may be below it.
- Try manual operation: if the pump runs from the panel but not when the float rises, investigate the automatic supply and switch circuit.
Some pumps use an electronic sensor or timed sensing rather than a separate float. Follow that model's test procedure; simply lifting the pump proves little.
Silent pump: test under load
Check the battery, labelled fuse, circuit breaker and panel switch. Automatic and manual feeds may have separate fuses, and the automatic feed may remain live with the main battery switch off.
Replace a blown fuse only with the manufacturer's specified rating. If it blows again, look for a jammed impeller, damaged wiring or a failed motor before trying another.
A multimeter reading with the pump disconnected can hide a corroded connection. Measure voltage directly across the pump's positive and negative leads with the pump switched on, then compare it with the voltage at the battery under the same conditions.
- Battery voltage healthy, pump voltage low: inspect fuse holders, terminals, switches and the negative return for resistance.
- Correct voltage but no operation: suspect a seized impeller or failed motor.
- Manual operation works: test the automatic feed, float switch and associated connections.
Green copper, loose crimps and connectors sitting in bilge water are common culprits. Renew damaged connections with properly crimped marine terminals and adhesive-lined heat-shrink, supported above the normal water level.