A sump pump is the one part of a waterproofing system with a motor, which means it’s the part that eventually fails — usually discovered at the worst possible moment. Here’s how to check whether yours is working, what the common failures are, and when to repair versus replace.
The short answer
Test it by pouring a bucket of water into the pit: the pump should kick on, clear the water, and shut off. If it won’t start, won’t stop, runs dry, or grinds, the usual culprits are a stuck float, a clog, lost power, or a worn impeller. Pumps last about 7–10 years, so an old, struggling one is often due for replacement — and a battery backup is worth adding either way.
Test it in two minutes
Slowly pour a five-gallon bucket of water into the sump pit until the float rises. A healthy pump switches on, pumps the pit down, and shuts off by itself. Watch and listen: no start, no shut-off, running without moving water, or grinding all point to a problem.
Common causes, easiest first
- Lost power: unplugged, tripped breaker, or a dead backup battery. Check this first.
- Stuck float switch: the float is jammed against the pit wall or debris, so it never triggers. Free it and test again.
- Clogged pit or intake: silt and debris block the screen. Clean the pit.
- Frozen or blocked discharge: water can’t get out, so the pump runs against a wall. Clear the line; add a freeze-protection fitting.
- Failed impeller or motor: runs but moves no water, or won’t run at all. Often the end of the pump’s life.
The failure that causes flooded basements isn’t usually the pump — it’s the power. The storm that overwhelms your basement is the same storm that knocks out the grid. A battery backup is the single highest-value add-on for a sump pump, because it runs precisely when the mains pump can’t.
Repair or replace?
A stuck float, a clog, or a blocked discharge is a cheap fix — do it. But if the pump is 7–10+ years old, runs without moving water, or has already failed once, replace it rather than nurse it. A new pump is inexpensive next to one flooded basement, and replacement is the smaller of the two waterproofing jobs. See our French drain vs sump pump guide for how it fits the whole system, and sump pump costs by city for local pricing and pros.
Frequently asked questions
- How do I know if my sump pump is working?
- Pour a bucket of water into the sump pit. The float should rise, the pump should switch on, pump the water out, and shut off on its own. If it doesn’t turn on, doesn’t shut off, runs but doesn’t move water, or makes grinding noises, it needs attention before the next storm.
- Why did my sump pump stop working?
- The most common causes are a stuck float switch, a clogged pit or intake, a tripped breaker or unplugged unit, a jammed or failed impeller, or a frozen/blocked discharge line. Age matters too — pumps wear out in roughly 7 to 10 years, so an old one that’s struggling is often just done.
- Do I need a battery backup sump pump?
- Strongly recommended. The storms most likely to flood a basement are also the ones most likely to cut power, and a mains-only pump is useless in an outage. A battery backup (or a water-powered backup) keeps it running exactly when you need it most.