Bilge Pump Troubleshooting

Story And Photos By Mark Corke

You'll need to fix it pronto, before heading out, and perhaps at the ramp. Here's how to find the problem and solution quickly.

Bilge pumps are the unloved cousins of boats. No one gives them much thought until they fail to operate, and then you could be, literally, sunk! There are only a few things that can go wrong with an electric bilge pump, as there are limited components. This flow chart will help you check each component, find the problem, fix it, and get on your way again as swiftly as possible.

Most pumps have an automatic float switch that detects when water is in the bilge, and automatically turns on the pump. There should also be a switch at the helm to override the automatic float switch, enabling you to turn on the pump manually. (There are other types of pumps not covered here that may present different issues, but this example should cover most contingencies.)

Small amounts of water in the bilge are normal, so don't sweat it if you see a little puddle in the bilge. But any more than an inch or two could be a problem. Get to know your boat and find out what's normal; a rising water level should be investigated without delay.

  • 1. Helm Switch

    Helm switch

    2. Float Switch

    Float switch

    1. Try the manual switch at the helm. If the pump runs, then the problem is most likely with the float switch.

    2. Check the float switch for debris in the bilge preventing it from operating. If you find any, clear the dirt away, turn helm switch back to automatic, and lift float switch to check operation.

  • 3. Battery

    Battery switch

    4. Fuse


    3. Check that the battery switch is in the "on" position if pump doesn't operate with the helm switch in either manual or auto modes. With the battery turned on, check to see if any of the other electrical equipment operates. If not, then the battery may require charging.

    4. If the battery switch is on and other equipment operates, the fuse may have blown. Replace with a new fuse of the correct rating after checking for cause. Bilge pumps are often connected directly to the battery. Check battery connections and correct if loose or corroded.

  • 5. Wiring

    Poor wiring

    6. Short/Overload

    Burnt pump

    5. Check all visible cables for signs of corrosion or breaks. If wiring looks good but pump still won't run in automatic with float switch elevated, the switch may need replacement. Wire nuts like these have no place on board. Use crimped connections.

    6. If there's a burnt smell in the vicinity of the pump or it's hot to the touch, then this could indicate an internal short or an overload caused by a jam. Disconnect pump from battery and replace.

  • 7. Impeller


    8. Screen

    Pump screen

    7. With power off and the pump withdrawn from its mounting bracket, try to turn the impeller by hand. It should rotate freely with a finger. If impeller can't be turned and there's nothing visible jamming the impeller, then pump is most likely in need of replacement.

    8. While the pump is removed from the bracket, clear the screen of any dirt, hair, or debris that prevents water from reaching the impeller.

9. Outlet Hose

If pump runs but very little water comes out, this could be caused by low battery voltage. Another cause could be a kinked, split, partially disconnected, air-locked, or blocked discharge hose. Check hose and reroute, reconnect, or replace as required.


When you have a bilge-pump problem, start at the top of this troubleshooting guide and work your way down until you've found and fixed it. If you get to the bottom and still haven't fixed or, at the very least, diagnosed the problem, then you may need the help of a qualified technician or access to electrical test equipment. 

— Published: April/May 2016

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