How to Test and Clean Your Bilge Pump and Float Switch

Locate each pump, its float switch, the helm switch, the fuse or breaker, and the discharge fitting on the hull. Write down the pump size (GPH) and location. Shower and fish-box sump pumps count too.

Check for fuel smell, oil sheen and debris. Oil and dirt make sludge that clogs pumps and jams float switches. Soak up any oil with absorbent pads and dispose of them properly. An oil-absorbent bilge sock or pad left near the pump (not touching the float) keeps catching small drips between checks; Massachusetts' clean boating program recommends one, and it should be replaced when it gets dark and heavy. If there is more oily water than pads can handle, have it pumped out at a marina instead of running the bilge pump.

Most small pumps have a strainer base. Squeeze the release tabs (or remove the screws) and lift the motor cartridge off the base. Clear out hair, zip-tie ends, leaves and sludge. Clean the impeller opening with a small brush. Snap it back together firmly.

Lift the float or flapper by hand. It should move smoothly and not catch on hoses, wires or the hull. BoatUS recommends mounting it fore and aft with the hinge forward and the float pointing aft, so surging water on takeoff does not damage it.

Turn the helm bilge switch ON. The pump should run. Turn it OFF.

Pour water (bucket or hose) into the bilge until the float rises. The pump should start on its own, pump the water down, and shut off when the float drops. If you cannot add water, lift the float by hand for a quick check, but a real water test is better.

Have a helper watch the discharge fitting outside the boat, or check it yourself. You want a strong stream. A weak dribble means a clogged strainer, a kinked or cracked hose, a worn pump, or low battery voltage.

Run your hand along the discharge hose. Look for kinks, cracks, soft spots and missing or rusted clamps (use stainless marine clamps). The fitting where the hose leaves the hull should be well above the waterline, or the hose should loop high (BoatUS suggests at least 18 inches above the waterline) so water cannot siphon back in. Remove any check valve in the line; BoatUS advises against them because they can stick or clog.

BoatUS notes most bilge pump failures come from corroded connections. Look for green corrosion, electrical tape, household twist-on connectors, or splices sitting in bilge water. Proper repairs use heat-shrink connectors placed as high as possible. Check the pump fuse is the size the pump maker specifies. Never replace a blown fuse with a bigger one or bridge it with wire; if the same fuse keeps blowing, a chafed wire or a jammed pump is likely, and that needs fixing first.

The pump and switch should be screwed or clipped down firmly. Mounts can crack from vibration. A pump that tips over will not pick up water.

If you have them, raise the water (or lift the higher float) until the backup pump runs and the alarm sounds. Alarms should be loud enough to hear over the engine.

Record the date and results in BoatMend. Keep a spare pump or motor cartridge, a fuse and a few connectors aboard.

Finding where the water comes from: if the pump keeps cycling, note whether it happens after rain or every day regardless of weather, then check the usual suspects with the boat at rest: rain getting past hatches and cockpit drains, the hull drain plug, livewell and washdown plumbing, hose clamps on through-hull fittings, a sterndrive's rubber bellows, the shaft seal on inboards, and the engine's exhaust and cooling hoses. A dry paper towel held against each suspect fitting shows a slow drip quickly.