A sump pump is the only machine in your house whose whole job is to work perfectly on the one night a year it's sitting underwater, the power's flickering, and you're asleep. Every other appliance can fail on a Tuesday and cost you a sandwich. This one fails on the night of the storm and costs you the basement. So when it goes quiet or starts humming as the water rises, the fear is total and the instinct is to rip it out and buy a new one right now.
Here's the reframe that saves the panic-buy — and, first, keeps you safe. A sump pump is not a magic water-remover you either have or don't. It's a four-link chain: it needs POWER, a FLOAT has to tell it to run, an IMPELLER has to be free to fling the water, and the water has to be able to GET OUT through the discharge pipe. "The pump is dead" is almost always one of those four links broken — and three of the four are free or nearly free to fix. The motor itself, the expensive part, is usually the last thing to fail, not the first. A new pump wired to the same stuck float, dropped into the same gravel, or plumbed to the same blocked pipe does the exact same nothing.
Read this before you reach into the pit: water plus electricity is the real danger
Everything else on this page is about money. This part is about your life, so it goes first. If the pit is filling or the floor is wet and the pump is misbehaving, the instinct is to reach down and grab it, wiggle the float, yank the plug. Do not put your hand into standing water around a pump that still has power to it.
The reason is specific, not vague fear-mongering. A sump pump lives in water and ages in water, and if a fault inside it lets electricity leak to its metal housing, that fault energizes the housing and the water around it. Electrical-safety guidance is blunt about this: a flooded basement can become, in their words, a "death trap," because touching the pump or the water can then deliver a fatal shock. That's the whole reason code now works the way it does.
The GFCI is protecting you — do not defeat it
Under the 2020 National Electrical Code, sump pumps within the usual household voltage and current range require GFCI (ground-fault) protection — the outlet or breaker that snaps off the instant it senses current leaking to ground. That device is exactly what stands between you and the energized-water scenario above.
Which sets up the single most dangerous "fix" people reach for. When a GFCI keeps tripping during a storm, the pump keeps losing power at the worst moment, and the temptation is to plug the pump into a regular, non-GFCI outlet so it "just stays on." Don't. A GFCI that trips repeatedly on a pump sitting in water is often telling you the pump is starting to leak current — the early warning of the death-trap fault. Bypassing it doesn't fix the pump; it removes the one thing protecting anyone who steps into that basement. The honest answer to "the GFCI keeps cutting my pump" is not to defeat the GFCI — it's a battery backup pump, which keeps you dry through both nuisance trips and the power outage a storm brings, without ever removing your shock protection.
The one real test: a bucket of water (and the fault that isn't a fault)
The only honest test of a sump pump is to slowly pour a few gallons of water into the pit and watch: the float should rise, the pump should kick on, the water should drop, and the pump should shut off cleanly. That is the whole test, and it's the single most valuable thing you can do for a sump pump — because it's the only way to catch the two faults below before the night you need it. Do it on a calm day, not mid-storm.
Now the correction that stops you from condemning a healthy pump:
- "It hasn't run all summer — it must be dead." Not necessarily. In a dry stretch the pit legitimately never fills high enough to lift the float, so a healthy pump correctly does nothing for months. Silence in July is not a diagnosis. Pour the bucket — that's the test. (But heed the flip side: a pump that sits bone-dry and unused for a whole season is exactly the one that seizes or air-locks when it's finally asked to run. The summer of silence is why you test in September, not why you assume it's fine.)
- "There's always a little water in the bottom — it must be leaking." No. A sump pump can't pull the pit bone-dry; it shuts off when the float drops to its "off" point, which leaves an inch or two behind by design. A damp pit floor between runs is normal, not a fault.
Sort the symptom into one of three families
Everything a "won't pump" sump pump does falls into three buckets. Find yours, and the cause list under it is short.
Family 1 — SILENT: no sound at all, no water moving
Silence means the motor isn't getting the "go" signal. That's a power problem or a float problem — both usually free.
- No power reaching it. Check the GFCI outlet (press reset) and the breaker. A tripped GFCI is the number-one reason a "dead" pump is silent — and see the safety section above about why it tripped before you just reset and forget it.
- The piggyback plug. Most float switches use a stacked "piggyback" plug: the float's plug piggybacks onto the pump's plug, and the pump's plug seats into the back of the float's. If that's knocked loose — or someone plugged the pump straight into the wall, cutting the float out of the circuit — the pump can't be switched on by the float at all. Reseat it in the switched position.
- The float is stuck DOWN. A tethered or vertical float that's jammed against the pit wall, wedged under the discharge pipe, tangled in its own cord, or pinned by debris can't rise to trigger the switch. The water climbs right past it. Free the float so it swings/rises through its full travel, and give it room from the wall.
Family 2 — HUMS: it's getting power, but no water moves
A steady electrical hum with no pumping means the motor is energized and trying, but the impeller can't turn or the pump can't grab water. This is the most-misread family — the hum sounds like a motor dying, and it's usually the opposite.
- Jammed impeller. The impeller is the little finned wheel that flings the water out. Grit, gravel, a pebble, or a chip of concrete from the pit can wedge it so it physically can't spin — the motor hums against a locked wheel. This is extremely common after a pump has sat dry and debris has settled around it. With the power off at the panel, lift the pump, pull the bottom screen/base, and clear whatever's fouling the impeller.
- Air lock. If the motor hums (or runs) but the water level won't drop and the pit had gone dry, air can be trapped inside the pump housing so it spins water-less — it can't prime itself. The designed cure is a small anti-air-lock "weep hole" drilled in the discharge pipe just above the pump and below the check valve; if yours is missing or clogged, the pump can vapor-lock. (That weep hole is supposed to trickle a little — more on that in the runs-constantly page.)
- Do not let it sit and hum. A stalled, humming motor is drawing heavy locked-rotor current and making heat with no water to cool it. Cut the power and clear the jam — leaving it to hum is how you turn a free fix into an actually-burned-out motor.
Family 3 — RUNS but the water keeps rising
The motor spins, you hear it working, and the level still climbs. The pump is fine; the water can't get out.
- Blocked or frozen discharge. The pipe that carries water out of the house is the wall it's pushing against. In a Mid-Atlantic cold snap the exposed discharge line or its outdoor outlet can freeze solid; the rest of the year it can be crushed, kinked, clogged with sediment, or plugged by ice or debris at the outlet. The pump runs, the water has nowhere to go, and it falls right back into the pit. A bigger pump just pushes harder against the same closed door.
- Air lock (again). The same trapped-air problem as Family 2 can present as "running but not moving water." Check the weep hole.
- Broken impeller or coupling. Rarely, the impeller has cracked or spun free of the shaft, so the motor turns but nothing flings the water. This is one of the few genuine "the pump has failed" cases — but confirm it only after you've ruled out the free blockages above.
The cruel part: every instinct here makes it worse or costs more
This is why the category is so misdiagnosed — the natural move in each case feeds the failure you're afraid of:
- It hums → "the motor's shot, buy new" → it's a pebble in the impeller or an air lock. Free to clear — and letting it hum while you shop is what finally cooks the motor you assumed was already dead.
- It's silent → "dead pump" → a tripped GFCI, a knocked-loose piggyback plug, or a float pinned against the wall. All free, all thirty seconds — and a new pump plugs into the same tripped outlet.
- It runs but the water rises → "it's too weak, buy a bigger one" → the discharge is frozen or blocked. A bigger pump pushes harder against the same wall and still floods you.
- The GFCI keeps tripping → "bypass it so it stays on" → you've removed your shock protection over water that may be carrying current. This is the one that isn't about money at all.
Match the symptom before you spend a dollar
Cheapest-and-likeliest first. Notice how far down the table you get before "new pump" is ever the answer.
| What you notice | Likely cause | First move | New pump? |
|---|---|---|---|
| Dead silent, water rising, no sound at all | Tripped GFCI / breaker, or piggyback plug loose | Reset GFCI & breaker; reseat the piggyback plug (and find why the GFCI tripped) | No |
| Silent though the pit is full; float looks stuck low | Float jammed against the wall / tangled / wedged | Power off at panel; free the float through its full travel; move it off the wall | No |
| Hums, no water moves | Jammed impeller (grit/gravel) or air lock | Power off; clear the impeller; check/clear the weep hole. Don't let it keep humming. | No |
| Runs hard but water keeps climbing | Discharge frozen, kinked, clogged, or air-locked | Clear/thaw the discharge line and outlet; check the weep hole | No |
| Hasn't run all summer; you're not sure it works | Untested, not necessarily broken | Pour a bucket in and watch it cycle — the only real test | No (test it) |
| Power on, float good, impeller clear — still won't run or won't move water | Genuinely seized/burned motor or broken impeller | Confirm, then replace — see the buying guide | Yes |
| Pump is 7–10+ years old and you rely on it | Age — sump pumps wear out on a clock | Replace proactively, before it fails in a storm (see below) | Yes (planned) |
When it really is the pump — and the one honest "replace it even though it might still work"
Two rows in that table say "Yes," and they're worth naming clearly so you don't over-repair a pump you can't trust.
The first is the genuine failure: power is reaching it, the float moves freely, the impeller is clear and turns by hand with the power off — and it still won't run, or the impeller has cracked or spun free so the motor turns but no water moves. That's a real dead pump. Replace it, and use the capacity, switch, and backup buying guide to size the new one to your water table rather than to the box's biggest number.
The second is the one case in this whole family where we'll tell you to replace a pump that might still limp along: age. Plumbers, insurers, and manufacturers broadly put a sump pump's service life somewhere around seven to ten years — and heavy-cycling pumps can wear out sooner, some in as little as a few years (verify against your own model and how hard it runs). Unlike almost everything else we write about, the honest advice here is not "run it till it dies." A sump pump that dies mid-storm doesn't cost you the pump — it costs you the basement, the drywall, and the mold, on the one night you can't get a plumber. If yours is past that window and you're leaning on it to protect a finished basement, replacing it on a dry afternoon is the cheap version of this problem. Waiting is the expensive version.