Why is my boat's bilge pump not working, and how can I troubleshoot it?
The electric bilge pump on my 32-foot cruiser has stopped clearing the bilge. Sometimes I hear it humming, but lifting the float switch does nothing on other occasions. How can I tell whether the pump, switch or wiring needs replacing?
Answer
Most bilge pump failures come from a blocked strainer, a jammed float switch, a lost electrical supply or corroded wiring. Try the manual override first, then follow the checks below before buying a replacement.
Check water level and power
If water is rising, start the manual bilge pump and find the source immediately. Ordinary bilge pumps are not designed to control serious flooding. Check the manual pump's intake strainer too, as debris can disable both systems.
Isolate the supply before handling wiring or opening the pump. Stop electrical testing if you smell petrol or find fuel in the bilge.
Make sure you have identified the bilge pump. A shower sump pump is a separate system, often inside a covered box, and may need several panel switches turned on before it operates.
- Check the battery charge, bilge pump fuse or breaker, and panel switch position.
- Try the manual override briefly while watching and listening at the pump.
- Lift the float fully, or use the automatic pump's specified test control.
Wiring varies between boats. Some need the battery switch, main breaker and bilge breaker all switched on. Others have a separately fused automatic feed connected ahead of the battery isolator. Trace yours before assuming the main battery switch also isolates the pump.
If a fuse has blown, check for jammed parts and damaged wiring before fitting the manufacturer's specified replacement. Never increase the fuse rating to keep the pump running.
Silent pump: switch and voltage
If manual override works but automatic operation does not, check the float switch, automatic feed and their connections. Remove cable ties, dirt or loose gear restricting the float. Check that it moves freely without touching a hose or bulkhead.
A float can move freely even when its internal contacts have failed. With power isolated, disconnect it and test continuity across a simple two-wire mechanical switch while raising and lowering the float. Electronic sensors need the manufacturer's test procedure.
Set a multimeter to DC volts and measure across the pump's positive and negative connections while it is commanded to run and remains connected. A disconnected wire can show normal voltage through a connection too corroded to carry motor current.
- No voltage: work back through the switch, fuse holder, breaker and supply connections.
- Voltage substantially below battery voltage: check both positive and negative wiring for resistance, particularly wet joints and loose terminals.
- Voltage close to battery voltage but no movement: suspect a seized mechanism or failed motor.