First, define the problem. A healthy pump cycles: it runs for under a minute, empties the pit, and rests — sometimes for hours. Running constantly means one of two patterns: the motor hums for minutes on end without the water level dropping, or it kicks on every minute or two around the clock, even when it hasn't rained in days. Both patterns wear the pump out fast, and both have a short list of causes. Start with the free checks. If you've never watched yours run a full cycle, the bucket method in our guide to testing a sump pump is the fastest way to see what normal looks like.
Time it. Stand at the pit for a few minutes. How long does the pump run, how long does it rest, and does the water level actually fall while it runs? A pump that runs and lowers the water is fighting inflow. A pump that runs while the level sits still is fighting a mechanical problem. That one observation splits the diagnosis in half.
Watch the float at shutoff. When the pump stops, does the water stop with it, or does the level climb right back up within seconds? Water that surges back into the pit the moment the motor stops is the signature of a failed check valve — the whole column of water in the discharge pipe is draining home.
1. A float stuck in the on position. The most common cause, and the cheapest. The float has wedged against the pit wall, tangled in its own cord, caught on the discharge pipe, or settled into silt. Unplug the pump, lift the float by hand, and let it drop — it should swing freely through its full arc with nothing touching it. Clear debris, untangle the cord, and reposition the pump so the float has room. Pits that are too small for the float's swing cause this again and again.
2. A failed check valve. The check valve sits in the discharge pipe and stops pumped water from flowing back when the motor stops. When it fails, the pump empties the pit, the water in the pipe falls back in, the float rises, and the pump empties the same water again — forever, every few minutes. Listen at shutoff: a working valve closes with a soft clunk; a failed one lets you hear water rushing back down. A replacement valve typically costs $15–$30 and swaps in with basic tools.
3. Inflow the pump can't beat. Sometimes the pump is fine and the water is real: a high water table, spring thaw, or days of rain can push groundwater in faster than a standard pump moves it out. Two sneaky versions of this one: a broken or leaking water line near the house, which explains a pump that runs constantly in dry weather, and a discharge pipe that dumps its water right next to the foundation — the pump then re-pumps its own output in an endless loop. Walk outside and see where the discharge actually lands; it should exit well away from the house and drain downhill.
4. An undersized or worn-out pump. A pump that's too small for the inflow never lowers the water far enough to trip the float off. A worn pump does the same thing more slowly: a silt-chewed impeller or a clogged intake screen moves half the water it used to. Pull the pump (unplugged), clear the intake, and check the impeller for damage. If the pump is past 7–10 years old and struggling, replacement beats repair — the motor has already lived most of its life.
| Cause | The tell | The fix | Rough cost |
|---|---|---|---|
| Float stuck on | Pump runs with the pit nearly empty; float hangs up | Free, clean, or reposition the float | $0 (a float switch alone runs $15–$40) |
| Check valve failed | Water rushes back and the level rebounds at shutoff | Replace the valve | $15–$30 for the part |
| Discharge recycling | Constant running that tracks the pump's own output | Extend the discharge away from the house | $20–$60 in pipe and fittings |
| High water table / heavy inflow | Runs hard in wet weeks, rests in dry ones | Bigger pump or a second pump | $150–$450 for the pump |
| Pump worn or undersized | Level barely falls while the motor runs | Replace the pump | $150–$450 DIY, $400–$900 installed |
Sump pumps are built for intermittent duty — short runs with long rests, so the motor cools between cycles. Constant running removes the rests. The motor overheats, the switch cycles far beyond its rating, and a pump that would have lasted 7–10 years in normal service can burn out in a single wet season of nonstop running. That's the real urgency here: a pump that runs all the time isn't just noisy, it's spending its whole lifespan in weeks. And a pump that dies mid-storm is exactly the scenario a battery backup sump pump exists for — worth deciding on while the primary still works, not after it quits.
Float, valve, inflow, pump — check them in that order and you'll find the cause in most pits within half an hour, usually for the price of a check valve. If the diagnosis ends at the pump itself and your pit does heavy work every spring, sizing the replacement is worth a few minutes of thought; our guide on whether a basement needs a sump pump covers matching pump capacity to how much water a pit actually sees.
Short, frequent cycling almost always means the check valve has failed. The pump empties the pit, the water standing in the discharge pipe drains straight back in, and the float rises again. Listen at shutoff for water rushing back down the pipe — that sound confirms it.
Three usual suspects: a high water table still draining after earlier rain, a leaking water line or irrigation line near the foundation, or the discharge pipe dumping water so close to the house that the pump re-pumps its own output. Dry-weather running that never stops deserves a close look at the water line possibility.
There's no single number — it depends on the motor and how hot it gets — but these motors are rated for intermittent duty, not continuous runs. Hours of nonstop running day after day is well outside the design, and a pump in that state is often measuring its remaining life in weeks rather than years.
It can be. During a major storm or spring thaw, inflow can be heavy enough that the pump runs most of the time and still holds the level. Judge it after the weather dries: a healthy system goes back to cycling with long rests. One that never rests, rain or shine, has a problem from the list above.
It tracks the cause. Freeing a stuck float costs nothing, a check valve is a $15–$30 part, and a replacement pump runs $150–$450 for the unit or $400–$900 installed by a plumber. The expensive version is the one where the pump burns out first and the basement floods — which is why the diagnosis shouldn't wait.