Why does my sump pump run constantly?
Updated August 2026
A sump pump that never shuts off, or cycles again seconds after it stops, is usually the victim of a stuck float switch or a failed check valve that lets the water it just pumped fall straight back into the pit. With a bad check valve, every cycle sends the vertical column of water in the discharge pipe right back down, so the pump keeps re-pumping the same gallons. With a stuck float, the switch never registers that the pit is empty. Both are cheap fixes ($15–40 for a new check valve). Left alone, constant running burns the motor out early, and a pump that dies mid-storm floods a basement.
Safety first: constant running is not just a nuisance, it is a countdown on the motor. Sump pumps are built to cycle, not run continuously, and a unit that never rests can burn out in weeks, leaving you with no flood protection right when a storm hits. Fix the stuck float or check valve promptly rather than listening to it grind for months. Keep the same water-and-electricity caution as any pump work: do not reach into a wet pit or handle the pump while it is plugged in, and cut power at the breaker if the floor is wet.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Stuck float switch (never resets to off) | Most common | Reposition or replace the float so it can drop fully and signal the pump to stop. | $15–40 |
| Failed or missing check valve | Most common | Water in the discharge pipe falls back into the pit after each cycle. Install a check valve with the arrow pointing away from the pump. | $15–40 |
| High water table or heavy rain | Common | Genuine inflow keeps the pit full. This is normal in a storm; a larger pump or a backup handles sustained load. | Varies |
| Pit too small or too shallow | Occasional | A small basin refills before the pump can rest. Enlarge the pit or widen the float on/off range so it cycles less. | $200–600 |
| Downspouts or drain tile flooding the pit | Occasional | Roof runoff or a footing drain routed into the pit keeps it full. Redirect downspouts and grade water away from the foundation. | $100–500 |
| Frozen or clogged discharge line | Occasional | Water cannot exit, so the pump runs against a blockage. Clear or thaw the outside discharge and add a slope or freeze guard. | $0–150 |
Check these first
- Watch a full cycle. If the pump shuts off but restarts within seconds, listen for water rushing back down the pipe.
- That rush-back sound is a bad or missing check valve letting the discharge column drain into the pit.
- Check that the check valve arrow points up and away from the pump, not backward.
- Lift and drop the float by hand to confirm it moves freely and actually shuts the pump off at the bottom.
- Note whether it started after heavy rain. Nonstop running during a real downpour can simply be a full water table.
Prevent it next time
The two cheap culprits, a worn check valve and a hanging float, are exactly what routine attention catches. When you clean the sump pit on schedule, verify the float swings through its full range and the check valve still holds water above it. Replace the check valve every few years as a wear item rather than waiting for it to fail. If your pit genuinely fills fast every storm, the answer is capacity and redundancy: size the pump to the inflow and add a maintained battery backup. And since constant running shortens life, track when the pump is due for replacement so you retire it before it quits.
When to call a pro
Call a pro when the pump runs nonstop even after you replace the check valve and free the float, when the pit is clearly undersized for the inflow, or when you suspect a high water table or failing drain tile feeding it. Enlarging a pit or reworking the drainage runs $200–600 and up, while a like-for-like pump replacement is $150–450. A pump that has been running continuously for weeks may already be near failure, so it is worth having its condition assessed before the next big rain rather than after.
Most of the causes above are maintenance problems wearing a disguise. OnOtto keeps the boring prevention on schedule so the 2 a.m. version doesn't happen.
Stop chasing symptoms, free for 30 daysFrequently asked questions
Is it normal for a sump pump to run constantly?
During a heavy storm or spring thaw with a high water table, yes, near-continuous running can be normal because real water keeps filling the pit. What is not normal is a pump that runs nonstop in dry weather, or one that shuts off and restarts within seconds. That short-cycling almost always means a failed check valve returning water to the pit, or a stuck float. If it runs constantly with a dry yard, start with those two cheap parts.
What does a check valve do on a sump pump?
A check valve is a one-way valve on the discharge pipe that keeps pumped water from flowing back down into the pit when the pump shuts off. Without it, the column of water standing in the pipe drains right back after every cycle, so the pump immediately senses a full pit and runs again, over and over. A new check valve costs $15–40 and installs in minutes with the flow arrow pointing away from the pump. It is the single most common fix for a pump that short-cycles.
Will constant running wear out my sump pump?
Yes. Sump pumps are designed to cycle on and off, and continuous running overheats the motor and accelerates wear, which can cut a 7–10 year life down to weeks or months. Worse, the failure tends to arrive during the very storm the pump is straining against. That is why a stuck float or bad check valve is worth fixing right away, not living with: the cheap part protects the far more expensive pump and the basement behind it.
How often should a healthy sump pump cycle?
There is no single number, because it depends on the water table and rainfall, but a healthy pump in dry conditions should sit idle and only kick on occasionally. During rain it may cycle every few minutes, running for 10–20 seconds each time and then resting. A pump that cannot get 10 or 15 seconds of rest between cycles in dry weather is short-cycling, and the check valve or float is the place to look first.