A bilge pump is the one circuit on a boat that has to work when nobody is aboard. It is also, on many boats, the circuit fitted with the cheapest connectors and left sitting in the dampest part of the hull.
There are two symptoms and they point in opposite directions: a pump that will not run, and a pump that cycles constantly. Neither should be ignored, and a pump that runs constantly should be treated as a possible ingress problem until proven otherwise.
Work in order, supply first, then control, then the pump itself. The permanent live feed, its inline fuse and the negative return are where most faults sit, because they are usually the oldest and lowest connections in the circuit.
If the manual override on the panel runs the pump but automatic does not, the fault is in the float switch or its wiring, not the pump.
A stuck float switch, a non return valve that has failed, or a discharge hose that loops in a way that lets water run back are the common mechanical causes. Electrically, a chafed float switch cable shorting to a live can hold the pump on.
If the pump is genuinely keeping up with real water coming in, that is a hull, stern gland or plumbing problem and it needs attention immediately, not a bigger pump.
Connections in a bilge need to be above the water line wherever possible, made in tinned marine cable, properly crimped and sealed with adhesive lined heatshrink. Domestic terminal blocks and twisted joints in this location fail, and they usually fail wet.
A bilge pump feed also normally stays live independently of the main battery switch, which means it must be fused close to the battery.
A pump cycle counter or a high water alarm turns an invisible slow leak into something you find out about early. On a boat left on a mooring, it is one of the more useful things you can add.
It is common practice for the automatic circuit to remain live with the isolator off, fused close to the battery, so the pump still works when the boat is left. How that is done on your boat should be checked rather than assumed.
Most often the joints rather than the pump, poor crimps in a wet bilge corrode within a season, and voltage drop then stops the pump lifting water.
On any boat left unattended, yes. It costs very little compared with what it protects and it tells you about a leak while it is still small.
We rewire bilge circuits in tinned marine cable with sealed joints, correct fusing and optional high water alarms.