Sump Pump Runs Constantly

A sump pump that runs nonstop or cycles on and off rapidly is usually caused by a stuck float switch, a check valve letting water flow back into the pit, an undersized pump struggling to keep up, or a genuinely high water table pushing in more water than normal. Identifying which one applies determines whether the fix is quick or requires a new pump.

1. Stuck or Misadjusted Float Switch

If the float switch is stuck in the “up” position—often from being jammed against the pit wall or tangled in its own cord—the pump keeps running even after the water level drops. Reposition the switch so it moves freely and re-test. This is a common cause of nonstop running and is covered in more detail in Sump Pump Float Switch Problems.

2. Rapid Cycling from a Faulty Check Valve

If the pump shuts off normally but kicks back on again within seconds, water may be flowing back down the discharge pipe into the pit through a failed or missing check valve, tricking the float switch into thinking the pit refilled. This creates a short-cycling pattern rather than continuous running, and is often accompanied by a distinct thud or bang each time the valve closes. See Sump Pump Check Valve Problems for how to check and replace the valve.

3. Undersized Pump for the Water Volume

A pump that’s too small for the amount of water entering the pit runs nearly continuously during wet weather because it can’t keep pace. This is more likely if the constant running started after a change in drainage, grading, or a particularly wet season, rather than appearing suddenly on an older pump. If sizing seems to be the issue, see Types of Sump Pumps for how pump capacity relates to pit and water volume, and Sump Pump Replacement for upgrading to a higher-capacity unit.

4. High Water Table or Heavy Inflow

During sustained heavy rain or seasonal snowmelt, it’s normal for a properly sized pump to run more frequently than usual. This isn’t necessarily a malfunction—if the pump keeps up and shuts off between cycles, it’s functioning as designed under higher water conditions. Constant running that continues well after weather conditions improve points back to a mechanical cause rather than water volume.

Diagnosing the Cause

1. Watch a full cycle: does the pump shut off and stay off, or restart within seconds?
2. Check the float switch for obstructions or improper positioning.
3. Inspect the check valve for backflow after the pump shuts off.
4. Consider whether the pump’s capacity matches current water conditions and whether recent weather explains the increased activity.

When to Repair or Replace

A stuck switch or bad check valve is typically a straightforward repair. Constant running due to an undersized pump usually calls for an upgraded unit rather than a repair. For general repair steps across sump pump issues, see Sump Pump Repair; if the pump is older or already showing other signs of wear, see Sump Pump Replacement.

For a full overview of sump pump problems and how they relate to each other, see the Sump Pump Problems Guide.

Safety note: Keep hands and tools away from an energized sump pit. Disconnect power before touching the pump, float, check valve, piping connections, or other components. Do not work on electrical equipment in or near standing water.