Sump Pump Not Working? Troubleshoot It Before the Next Storm
A dead sump pump only reveals itself when the basement floods. Here's how to test and troubleshoot yours — and fix the common failures — before you need it.
A sump pump is the definition of out-of-sight, out-of-mind — until a storm hits, the basement floods, and you discover it died months ago. Because it sits silent for long stretches, the only way to trust it is to test it on a schedule and know how to troubleshoot the common failures. Here's how.
First: how a sump pump should behave
Water collects in the sump pump pit; when it rises, a float switch trips the pump on; the pump pushes water up and out a discharge pipe away from the house; a check valve on that pipe keeps the pumped water from draining back in. When any link in that chain fails, you get a pump that won't start, won't stop, or runs but moves no water.
The bucket test (do this first)
This is the test the sump pump task, and it diagnoses most problems in two minutes:
- Slowly pour a bucket of water into the pit until the float rises.
- The pump should switch on, pump the pit nearly dry, and shut off on its own.
What you see tells you where to look next.
It won't turn on
1. Check power. Confirm it's plugged in and the outlet is live. Sump pumps often share a GFCI outlet that can trip unnoticed, or a breaker that's tripped — see how to reset a circuit breaker. Many pumps use a "piggyback" plug; make sure both the float plug and pump plug are seated.
2. Free the float. A stuck float is the most common mechanical failure. If it's wedged against the pit wall, tangled, or waterlogged, it can't rise to trigger the pump. Reposition it so it swings freely.
3. Suspect the motor. If it has power and a free float but stays silent (no hum), the motor has likely failed. Most pumps last 7–10 years; replacement is the fix.
It runs but won't stop
- Stuck float in the "on" position — reposition it.
- Missing or backward check valve — pumped water flows straight back into the pit, so it pumps forever. Confirm the valve's arrow points away from the pump.
- Clogged or frozen discharge line — the water has nowhere to go.
- Undersized pump for the water volume — it may need an upgrade.
Don't ignore this; continuous running burns out the motor fast.
It runs but moves no water
- Clogged intake screen at the base — clear debris and gravel.
- Air-locked pump — some need a small weep hole drilled in the discharge pipe to release trapped air.
- Clogged or disconnected discharge pipe.
Check the discharge line outside
Walk outside and confirm the discharge water exits well away from the foundation — not pooling against the house, where it just drains back into the pit. In winter, make sure the line hasn't frozen shut. This pairs with extend downspouts away from the foundation and good soil grading to keep water away in the first place.
Don't skip the backup
The cruel irony of sump pumps is that the storms most likely to flood your basement are the same storms most likely to knock out power. A battery backup (or water-powered backup) keeps the pit pumping during an outage. Test it along with the main pump — that's the test the sump pump backup battery task. For the full routine, see how to test a sump pump and the sump pump system overview.
Make it automatic
Build your free Owner Tools plan and we'll schedule the bucket test and backup-battery check before each wet season — so your pump is proven working before the water rises, not after. No login, no address required.