A sump pump that won’t turn on is almost always one of two things: it’s not getting power, or the float switch that’s supposed to trigger it is stuck or dead. Check those two first, in that order, before you touch anything else. Ninety percent of “dead” pumps are a tripped GFCI, an unplugged cord, or a float that can’t rise. The classic test settles it fast: pour a five-gallon bucket of water into the pit and watch. If the float rises and the pump kicks on, it works — your problem was upstream. If the water climbs and nothing happens, work down the list below. First, make it safe.
Likely causes, ranked
Start at the top — these are ordered by how often they’re the culprit. Most no-start calls end in the first three rows.
| Cause | How to tell | Fix |
|---|---|---|
| No power / tripped GFCI or breaker (start here) | Pump is silent, no hum. GFCI outlet button popped, or the breaker’s tripped. Cord knocked loose. | Reset the GFCI, reset the breaker, reseat the plug. Free. |
| Stuck float switch (most common mechanical cause) | Water’s high but the float is jammed against the pit wall, the pump body, or the cord — or sunk with debris on it. | Free the float, clear the pit, reposition the pump. Free. |
| Failed piggyback float plug | Float looks fine and moves, but the pump still won’t run when the float rises. | Bypass test (below). Replace the switch if the pump runs direct. |
| Clogged impeller or intake screen | Motor hums but won’t move water, or trips out. Grit, gravel, or a rag in the intake. | Clear the screen and impeller. Free. |
| Airlock (runs, doesn’t pump) | Pump runs but water level doesn’t drop. Air trapped in the pump housing. | Drill a 1/16″–1/8″ weep hole in the discharge pipe. Cheap. |
| Stuck or failed check valve | Pump runs but pit refills instantly, or water won’t leave. Valve installed backwards or gummed shut. | Check the flow arrow points up; clean or replace the valve. |
| Frozen or clogged discharge line | Pump runs, hums, or trips; nothing exits outside. Winter, or blocked outlet pipe. | Thaw or clear the line; check the exterior outlet. |
| Burned-out motor | Power’s confirmed good, float works, but the pump is dead silent or trips instantly. Often 7–10+ years old. | Replace the pump. Not repairable. |
How to diagnose it, step by step
- Run the bucket test. With power on, slowly pour a five-gallon bucket of water into the pit until the float rises. A working pump kicks on within a few seconds and drains it. If it runs and drains — the pump’s fine, and your issue was a tripped breaker or a float that had been stuck. If nothing happens, kill the power and keep going.
- Check the power. Is it still plugged in? Cords get bumped. Press the reset button on the GFCI outlet — these trip on their own and are the single most common “dead pump.” Then check the breaker panel and reset any tripped breaker. Plug a lamp or phone charger into the outlet to confirm it’s live. Plug the pump directly into the wall — never an extension cord, which drops voltage and overheats the motor.
- Inspect the float switch. Reach in only after power is off. The float is a ball or a vertical collar that rides up with the water. Make sure it moves freely and isn’t wedged against the pit wall, the pump, or its own cord. Clear any gravel, mud, or debris fouling it. Tethered floats need room to swing — keep at least 3 inches of cord between the ball and its mounting clip. Reposition the pump so the float has clearance.
- Test the piggyback float plug. Many pumps use a stacked “piggyback” plug: the pump’s cord plugs into the back of the float switch’s plug, and only the float plug goes into the outlet. The float is the most common part to fail. To test it, pull the pump’s cord out of the piggyback and plug the pump directly into the outlet. If the pump runs immediately, the motor is good and the float switch is bad — replace it. Don’t leave it running dry more than a minute or two; it’ll overheat. (No piggyback? Lift an integrated float to its “on” position with a broom handle — never your hand near a live pit.)
- Check the impeller and intake screen. Power off, pull the pump out of the pit. Flip it over and remove the intake screen on the bottom. Grit, gravel, and slime collect here and jam the impeller. Clear anything blocking it and make sure the impeller spins freely by hand. A humming pump that won’t move water often has a jammed or clogged impeller.
- Look for an airlock. If the pump runs but the water won’t drop, air may be trapped in the housing. The fix is a weep hole: drill a 1/16″ to 1/8″ hole in the discharge pipe just above the pump outlet and below the check valve, angled back into the pit. It lets trapped air escape so the pump can prime. A little water squirts from it on each cycle — that’s normal and by design.
- Inspect the check valve. The check valve on the discharge pipe keeps pumped water from draining back into the pit. Find the arrow stamped on its body — it must point up, toward the discharge, away from the pump. Installed backwards, it blocks flow. Gummed shut, it stops water leaving; stuck open, the pit refills the instant the pump shuts off and the pump short-cycles. Clean it or swap it.
- Check the discharge line. Follow the pipe to where it exits outside. In winter, the outdoor end freezes and backs the whole line up — thaw it and add a slope or an air gap so it drains. Any season, the outlet can clog with mud, ice, leaves, or a critter’s nest. Clear it so water has somewhere to go.
Tools & parts you’ll need
- Five-gallon bucket (for the test)
- Non-contact voltage tester (to confirm the outlet is dead before you reach in)
- Headlamp or work light
- Shop vac (to empty and clean the pit)
- Screwdriver and adjustable pliers
- Cordless drill and a 1/8″ bit (for the anti-airlock weep hole)
- Work gloves
- Replacement piggyback float switch (universal, if the float tests bad)
- Replacement check valve sized to your discharge pipe (usually 1-1/2″)
DIY cost vs. calling a pro
Typical US ranges for 2026; regional and brand variation applies. Most fixes here are free or a cheap part.
| Job | DIY parts cost | Typical pro cost |
|---|---|---|
| Reset GFCI / breaker, free a stuck float | $0 | $100–$200 service call |
| Clean pit, clear impeller / intake | $0 | $150–$300 |
| Drill a weep hole (fix airlock) | $0–$10 | $150–$250 |
| Replace float switch | $15–$40 | $150–$300 |
| Replace check valve | $12–$30 | $150–$300 |
| Replace the whole sump pump | $120–$350 (part) | $400–$800+ installed |
Difficulty & time
Bucket test, power check, freeing the float: beginner, 15–30 minutes. Piggyback test, cleaning the impeller, weep hole, check valve: intermediate DIY, 30–60 minutes. Swapping a float switch: intermediate, about an hour. Full pump replacement: intermediate-to-advanced, 1–2 hours — doable for a confident DIYer, but many homeowners hand this one off.
Call a pro — or replace the pump — if…
- Power’s confirmed good, the float works, but the pump is dead silent or trips the breaker instantly — the motor’s burned out. Replace it, don’t repair it.
- The pump is 7–10+ years old and acting up — it’s near the end anyway; replacing beats chasing failures. Our guide to choosing and sizing a replacement sump pump walks through it.
- The outlet is dead and won’t reset, or you see scorching, a melted plug, or water near the wiring — that’s an electrical job.
- Storms are coming and the pit is filling faster than you can diagnose. Bail it with a shop vac and get someone out.
- You want insurance against the next power outage — a burned motor or a dead breaker means nothing if a battery backup sump pump is standing by.
For the manufacturer’s own checklist, Pentair’s sump pump troubleshooting FAQ is a solid, no-nonsense reference.
FAQ
How long do sump pumps last?
About 7 to 10 years for a typical pedestal or submersible pump. Run time, water volume, grit in the pit, and cycle frequency all move that number. If yours is past a decade and starting to act up, plan a replacement rather than nursing it through the next storm.
Why does my sump pump hum but not pump water?
The motor’s getting power but something’s stopping it from moving water: a jammed or clogged impeller, an airlock, a stuck check valve, or a blocked discharge line. Kill the power, pull the pump, and clear the intake screen first — that’s the usual cause.
How do I test my sump pump?
Pour a five-gallon bucket of water into the pit until the float rises. A healthy pump switches on within a few seconds, drains the pit, and shuts off on its own. Do this a couple times a year, and always before storm season.
My float is stuck — can I just leave the pump plugged in and lift it by hand?
No. Don’t put your hand in a powered pit. Unplug the pump or kill the breaker first, then free the float. To bench-test an integrated float, lift it with a broom handle, never your fingers.
Should there be water coming out of a small hole on the discharge pipe?
Yes, if someone drilled a weep (anti-airlock) hole. A small spurt on each cycle is normal and stops the pump from airlocking. If there’s no hole and your pump runs without draining, drill one — 1/16″ to 1/8″, just above the pump and below the check valve.