What Is a Bilge Float Switch (Automatic Float Switch)?
A level switch that starts the pump when water rises in the bilge — the cheapest, yet one of the most vital, electrical parts on board.
A bilge float switch (automatic float switch) is the switch that starts the pump when the water level in the bilge rises, and stops it once the level drops again. It is often the first, and sometimes the only, part to notice water coming in while the boat is at rest. If the float switch fails, the pump will not come on.
The result is that a ‘small leak’ quietly becomes a rising bilge.
Common faults and testing
Sticking: Lint, bits of plastic bag and an oil film in the bilge can jam the mechanism either way: the pump may not start at all, or it may never stop (flattening the battery).
Oily bilge: An oil film can glue up a conventional float switch and confuse a non-contact sensor; a dirty bilge is a blind sensor.
Monthly test: Lift the float switch by hand and listen for the pump. If you hear nothing, the fault is usually one of three things: the float switch, the fuse, or the pump.
Golden rule: a clean bilge is essential if the float switch is to work properly. Cable connections that sit in constant damp also corrode green; even with a sound switch, the circuit can still be dead.