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Solved problems · Plumbing · Crew answer

Why won't my bilge pump turn on automatically?

A bilge pump that runs on manual but not on automatic usually has a stuck or failed float switch, or a break in its always-on wiring. Here's how to test it.

Symptom

Water collects in the bilge but the pump doesn't start by itself. It may still run when switched to manual at the panel.

Likely cause

Most automatic bilge pumps run through a float switch that closes as water rises. The float can be jammed by debris or a hose, or fail inside. The automatic circuit is often wired straight to the battery so it works with the main switch off, and its fuse, connections or wiring can corrode or break where they sit in damp bilges. Sometimes the pump motor itself has failed.

Stop now if

Water is rising faster than you can explain, or you can't find the source. Pump by hand or with another pump, find the leak, and call for help if you can't keep up. Don't leave the boat unattended until the automatic pump is working.

The fix, in short

  1. Test the pump on manual. Switch the pump to manual at the panel. If it runs, the pump and main wiring are fine and the fault is in the float switch or its circuit.

  2. Lift the float by hand. With the panel set to automatic, lift the float switch. The pump should start right away. If it doesn't, free any debris or hoses that stop it moving and try again.

  3. Check the always-on feed and fuse. Automatic bilge circuits are commonly fed directly from the battery so they keep working with the battery switch off. Check that circuit's fuse and connections.

  4. Test the switch with a meter. With power off, disconnect the float switch and check continuity. It should be open when down and closed when lifted. If it never changes, replace it.

  5. Fix wet connections. Move splices above the bilge water line where you can, and use sealed heat-shrink connectors. Wet connections corrode quickly and can also feed stray current into the water.

  6. Check the discharge. Make sure the discharge hose isn't kinked or blocked and has a vented loop or other siphon protection if its outlet can go under water when heeled.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Bilge: Electric bilge pump, float switch, panel switch, always-on fused feed and discharge hose

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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