Sump Pump Not Working? Tests to Run Before the Next Storm
Most sump pump failures come down to four things: a stuck float, a failed check valve, a jammed or worn motor, or no power reaching the pit. The fastest diagnosis is the bucket test: pour water in and watch. Here is how to find the cause before the next storm finds it for you.
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Safety first: if you smell gas, see water near electrical outlets or your panel, or sewage is contacting living areas, get people clear first. For a gas smell, leave and call 911 or your gas utility's emergency line before anything on this page.
- !Water in the pit is touching electrical cords, the outlet, or a power strip
- !You smell something burning from the pump or the motor is hot to the touch
- !The pit is overflowing and rising water is reaching the furnace, panel, or living space
- !The pump runs but you get a tingle or shock touching nearby metal or the water
- !Sewage, not clear groundwater, is coming up the pit (this is an ejector failure, not a sump)
- ✓Run the bucket test: slowly pour a 5-gallon bucket of water into the pit and watch the float rise. The pump should kick on and clear the water, then shut off
- ✓Confirm power: check that the pump is plugged in, the outlet has power, and the breaker or GFCI has not tripped. Many pumps use a piggyback plug that can come loose
- ✓Look at the float: reach in (power off) and feel whether the float is wedged against the pit wall, the pump body, or tangled in the discharge pipe
- ✓Check the discharge outside: make sure the line where it daylights is not frozen, crushed, or blocked by ice, leaves, or a stuck check valve
- ✓Listen on the next cycle: a pump that runs but the water does not drop, then refills, usually means the check valve is letting water flow back in
- →The bucket test shows the motor hums or buzzes but the impeller does not move water: a jam or a failed motor
- →The pump runs constantly and never shuts off, even after the pit empties: stuck float or failed switch
- →The pump cycles on and off rapidly every few seconds: failed check valve or a float set too low
- →You smell a musty or sewage odor from the pit on a sump (not ejector) system: standing stale water or a cracked pit
- →The pump is more than 7 to 10 years old and storm season is coming: replace before it fails under load
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Start with the bucket test
Before guessing, make the pump perform. Pour a five-gallon bucket of water slowly into the pit and watch the float rise. A healthy pump kicks on partway up, pumps the pit down, and shuts off cleanly. What you see in that thirty seconds tells you which branch you are on. Nothing happens at all: power or switch. It hums but no water moves: a jam or dead motor. It pumps then the water flows right back in: the check valve.
Do this test now, on a dry day, not during the storm that exposes the failure. A sump pump spends most of its life idle, which is exactly why a stuck float or a seized impeller goes unnoticed until the water is rising. Five minutes with a bucket once a season is the single most useful thing a homeowner does for a sump.
The float is the usual culprit
More sump pumps fail to start because of the float than for any other reason. The float is the switch: it rides up on the rising water and triggers the motor. Pits are tight, and a tethered float swings into the wall or the pump body and hangs up; a vertical float gets gunked or tangled in the discharge pipe. With the power off, reach in and feel whether the float moves freely through its full travel.
Clearing an obstruction or repositioning the float restores a surprising number of dead pumps at no cost. If the float moves freely but still does not trigger the motor on the bucket test, the switch itself has failed, which is a $150 – $300 service item rather than a new pump. A pump that runs nonstop and never shuts off has the opposite problem: the float is stuck in the up position or the switch has welded closed.
Runs but the water comes back: the check valve
The check valve is a one-way flap on the discharge pipe that stops pumped water from draining back down into the pit when the motor stops. When it fails, every cycle pumps water up the pipe and then lets most of it fall back in, so the pump runs, the pit briefly drops, and seconds later it refills and the pump kicks on again. That rapid short cycling wears the motor out fast.
You can often hear it: a clunk and a rush of water flowing backward right after the pump shuts off. A check valve is an inexpensive part and a quick replacement. If the discharge line outside is frozen or blocked instead, the pump may run, fail to push water out, and overheat, so check that the line daylights freely before assuming the valve. A pump that has overheated and shut off on its thermal protector points to that kind of blockage.
What each fix costs
The repair menu here is short and mostly affordable. A diagnostic service call to find and fix a stuck float, loose plug or blocked discharge runs $150 – $350. Replacing a failed float or switch runs $150 – $300. A new check valve is a small part and a quick visit. The numbers stay low because so many sump failures are switch and float problems, not dead pumps.
When the motor is the problem (it hums and will not turn, has burned out, or the pump is simply old), replacement runs $400 – $1,200 installed for a pump in an existing pit. If yours is past 7 to 10 years and storm season is close, replacing it on your schedule beats an emergency call during a flood. Our sump pump installation guide breaks down pedestal versus submersible and battery backup pricing so the replacement is the right one.
Storm-proof it before you need it
A sump pump only matters during the worst weather, and the worst weather is also when the power most often goes out. A primary pump on a dead circuit does nothing while the basement fills. That is the case for a battery backup, which keeps pumping for hours when the grid is down. Test both the primary and the backup with the bucket before each wet season.
Keep the discharge clear and sloped away from the foundation so it cannot loop back. Make sure the pit has a sealed lid and that the float has room to travel. If your sump has already lost the race and water has reached the floor, the cleanup and containment side, including when it is groundwater versus a sewage backup, is worth reading before you wade in.
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