Sump Pump Keeps Running: Float Stuck, Check Valve & High Water Table

Common Symptoms

• Pump runs without stopping even when the pit looks empty
• Pump shuts off but restarts within 30–60 seconds
• Pump motor is warm or hot to the touch
• Pump has been running for hours or days
• Discharge line is constantly flowing water

Most Likely Causes

1. 1

   Float Switch Stuck in 'On' Position (Most Common)

   A tethered float switch can get wrapped around the discharge pipe, wedged against the pit wall, or stuck in the up position by a corroded pivot. A vertical float switch can seize internally. In either case, the pump receives a continuous 'water is high' signal and runs without stopping, even with the pit empty.

2. 2

   Failed Check Valve Causing Back-Flow

   A check valve that fails in the open position allows water to drain back into the pit through the discharge pipe every time the pump shuts off. The pump empties the pit, shuts off, the check valve leaks water back in, the float rises, and the pump starts again — cycling every few minutes indefinitely. A failed check valve dramatically increases pump cycling and motor wear.

3. 3

   Discharge Line Draining Back into the Pit

   If the discharge pipe exits the house and terminates too close to the foundation, the discharged water percolates back through the soil into the drainage tile and back to the pit. The pump is pumping water from the yard back into itself. Discharge should terminate at least 10–20 feet from the foundation.

4. 4

   Genuine High Water Table or Heavy Inflow

   During extended rain, spring snowmelt, or on properties with a naturally high water table, the pit may genuinely be receiving more water than the pump can handle. The pump runs continuously because it's actually keeping up — barely — with constant inflow. This isn't a malfunction, but the pump is running at capacity and may need to be upsized.

5. 5

   Undersized Pump for the Application

   A 1/3 HP pump installed in a pit with high inflow may cycle continuously because it cannot keep up. Upgrading to a 1/2 HP or 3/4 HP pump, or adding a second pump, resolves this. Also check whether the discharge line is properly sized — undersized pipe creates back-pressure that reduces effective pump output.

Quick DIY Checks

1. 1Observe the float: look into the pit while the pump is running. The float should be in the down position when the pit is empty — if the float is still high or stuck up with an empty pit, it's triggering continuous operation. Manually push the float to the down position. If the pump shuts off, the float is stuck.
2. 2Free a tethered float: if the float is tethered (on a cord or arm), trace the tether to confirm it's not wrapped around the discharge pipe. Reposition the pump so the tether hangs freely and the float can swing to the bottom of the pit without touching anything.
3. 3Test the check valve: after the pump shuts off, immediately watch for water flowing back into the pit from the discharge pipe. If water starts returning within seconds of pump shutdown, the check valve has failed. Replace it with a PVC swing check valve of the matching pipe diameter ($10–$20).

1. 4Check where the discharge terminates: go outside and find where the discharge pipe exits the house. The water should be discharging at least 10 feet from the foundation, ideally to a sloped area or municipal drain. If it's discharging near a downspout or foundation, redirect it.
2. 5Measure the inflow rate: with the pump unplugged, watch the water level rise in the pit. Time how long it takes to rise 6 inches. Compare this to your pump's flow rate specification (gallons per hour at the rated head pressure). If the inflow rate exceeds the pump's capacity, upsize the pump.
3. 6Plug the pump into a separate outlet and bypass the float: plug the pump directly into an outlet and leave it running for a minute while the pit is full. If the pit drains and stays down, the pump is fine and the issue is the float or back-flow. If the pit level doesn't drop despite the pump running, the pump is failing or undersized.

Repair vs Replace

Recommended Tools & Parts

• PVC Swing Check Valve

  Swing check valve for sump pump discharge pipe — prevents back-flow into the pit after pump shutdown. Match diameter to your discharge pipe (typically 1-1/4" or 1-1/2").

  $10–$20

  Buy on Amazon →

• Sump Pump Float Switch Replacement

  Replacement float switch for submersible sump pumps. Tethered or vertical-style. Select based on your pit diameter and existing pump configuration.

  $15–$40

  Buy on Amazon →

• 1/2 HP Submersible Sump Pump with Float

  Mid-range 1/2 HP submersible pump — handles most residential water table conditions. Includes pre-installed integrated float switch.

  $120–$200

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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