How to Fix a Sump Pump: Not Turning On, Running Constantly, and Float Issues (2026)
A sump pump that won't turn on, runs without stopping, or hums without pumping has a failed float switch, a stuck or faulty switch, or a failed motor. This guide covers diagnosing and fixing each failure mode.
Sump pump won't turn on with water in the pit: (1) Manually lift the float — if the pump kicks on, the float switch is stuck or the float is waterlogged. Adjust or replace the float. (2) Pour a bucket of water directly into the pit to raise the level — if the pump still won't start, the float switch has failed or the pump motor is seized. (3) Check the outlet with another device — if the outlet is dead, reset the GFCI (most sump pumps plug into a GFCI outlet). Pump running constantly with no water: the float is stuck in the ON position, or the discharge line is blocked and the pump is recirculating water.
Frequently Asked Questions
How do I test a sump pump to make sure it's working?
Annual test procedure: (1) Find the pump in the pit — confirm the power cord is plugged into the outlet. (2) Slowly pour a 5-gallon bucket of water into the pit. The float should rise and trigger the pump. Watch for: the pump starts within 30 seconds of filling, water discharges through the pipe, the pump shuts off as the pit empties. (3) Manually lift the float to trigger the pump without pouring water — the pump should run while the float is elevated and stop when released. Best time to test: late winter before spring snowmelt, and early spring before the rainy season.
What is a float switch and how does it fail?
The float switch is the trigger mechanism that tells the pump when to run. Most residential sump pumps use a tethered float (a ball on a cord) or a vertical float (slides up a rod). When water rises, the float rises and closes a switch that starts the motor. Float failures: (1) Float gets tangled on the pump or pit wall — can't rise freely. Untangle and adjust the float cord length so the float can move up and down freely. (2) Float becomes waterlogged and sinks instead of floating — replace the float. (3) Float switch contacts fail — the switch won't close even when the float is in the correct position. Replace the entire float switch assembly.
The sump pump runs but water isn't going anywhere. What's wrong?
The pump is running but not discharging means: (1) The check valve (a one-way valve in the discharge pipe that prevents backflow) is stuck closed or has failed. The pump is recirculating water back into the pit instead of pushing it out. Remove the check valve and test if it opens freely — replace it if stuck. (2) The discharge pipe is frozen or blocked. Trace the discharge pipe to its exterior exit point — confirm it's clear and not packed with ice or debris. (3) The pump impeller is clogged with debris. Disconnect power, remove the pump, and check the impeller (the internal spinning disc) for mud, stones, or debris.
How long do sump pumps last and when should I replace it?
Sump pumps typically last 7–10 years, though pumps in wet climates with frequent cycling may wear out sooner. Replace rather than repair when: the pump is over 10 years old (even if currently working), the motor is making grinding or bearing noise, the pump runs but flow is noticeably weaker than before, or repairs have cost more than half the price of a new pump. A new pedestal or submersible pump costs $100–$300 — replacement is straightforward and takes under an hour. Having a backup pump (battery backup or water-powered) is worthwhile in areas with frequent flooding or power outages.
My sump pump runs every few minutes even in dry weather. What's causing that?
Frequent cycling in dry conditions usually means: (1) The check valve is not seating properly — water pumped out is flowing back into the pit, causing repeated cycling. Replace the check valve. (2) There's an underground water source feeding the pit continuously (high water table, underground spring, footing drain connection). If the pit never fully empties between cycles, the pump is working correctly — the issue is chronic high groundwater, not pump failure. Consider a higher-capacity pump or a secondary pump. (3) The discharge line is discharging too close to the foundation and the same water is re-entering the pit. Extend the discharge pipe further from the house.
Sump pump won’t turn on with water in the pit: (1) Manually lift the float — if the pump kicks on, the float switch is stuck or the float is waterlogged. Adjust or replace the float.
Test the sump pump every spring before the rainy season — don’t find out it’s failed during a flood.
What you need
- 5-gallon bucket (for testing)
- Replacement float switch ($15–$30 if float is the issue)
- Replacement check valve ($10–$20)
- Screwdriver and pliers
Step 1: Test the pump
Pour a 5-gallon bucket of water into the sump pit. Watch the float rise. The pump should start within 30 seconds, discharge water, and shut off as the pit empties.
If the pump doesn’t start: lift the float manually. Pump starts = float stuck/failed. Pump still doesn’t start = power issue or motor failure.
Step 2: Check power
Confirm the pump is plugged in. Trace the cord to the outlet — most sump pumps use a GFCI outlet. Find the GFCI (may be located elsewhere in the basement or garage, not directly next to the pump) and press TEST then RESET.
Step 3: Fix a stuck or failed float
If the float is tangled: reach into the pit and free it, then adjust the float cord or tether so the float can move up and down freely without catching on the pump or pit wall.
If the float is waterlogged or the switch doesn’t trigger even when float is elevated: replace the float switch assembly. Most are model-specific — note the brand and model (label on pump body) when ordering.
Step 4: Check and replace the check valve
The check valve is a section of the discharge pipe — typically 12–18 inches above the pump. It has a directional arrow stamped on it. Test it by pouring water into the pit while the pump is running — listen for water draining back into the pit after the pump stops. If you hear it: the check valve has failed. Shut off power, disconnect the check valve from both sides, and install the replacement.
Step 5: Replace the pump
If the motor hums but the pump doesn’t discharge (impeller seized), or the motor makes grinding noises: replace the pump. See How to Install a Sump Pump for the full replacement procedure.
Related guides
- How to Install a Sump Pump — full replacement pump installation
- How to Fix a Basement Leak — addressing the water source that feeds the sump pit
- Basement Waterproofing Cost — professional drainage system installation
- Best Portable Generators for Home Backup — keep the pump running when power goes out
- Test the pump manually
Unplug the pump. Plug it back in directly — if it runs and pumps water, the pump motor is working and the problem is the float switch. If it hums but does not pump: the impeller is jammed with debris. If it is completely silent when plugged in: the motor has failed or there is no power. Check the GFCI outlet or circuit breaker serving the sump pit. Press the GFCI test/reset button. A tripped GFCI is a common cause of a pump that appears dead.
- Fix a stuck float switch
The float switch triggers the pump when water rises in the pit. A float that is stuck in the down position means the pump never turns on; a float stuck in the up position means the pump runs constantly. Reach into the pit and check the float — it should move freely up and down. If the float is tangled on the discharge pipe or against the pit wall: reposition it so it swings freely. For tethered floats: adjust the tether length to ensure the float rises before water reaches the pump motor. For vertical floats: check the float rod for debris or corrosion that prevents smooth travel.
- Clean the pump inlet and impeller
A pump that hums but doesn't move water has a blocked impeller. Disconnect the pump from the discharge pipe (unscrew the coupling). Remove the pump from the pit. Flip it upside down and remove the bottom screen or cover. Use a stiff wire or small screwdriver to clear gravel, debris, or hardened mineral deposits from the impeller cavity. Rinse under running water. Reinstall and test — water should pump freely within seconds of the motor starting.
- Test the check valve
The check valve on the discharge pipe prevents pumped water from flowing back into the pit when the pump stops. A failed check valve causes the pump to run frequently (water drains back, pit fills, pump runs again in a cycle). Test: after the pump runs and stops, listen for a gurgling or rushing sound from the discharge pipe (water flowing back). If present: the check valve disc or flap has failed. Replace the check valve — it unscrews or is held by two hose clamps and costs $10–$20.
- Replace the pump
If the motor is burned out (no sound when plugged in with power confirmed, or smoke/burning smell): replace the pump. Note the current pump's horsepower (1/3 HP handles most residential pits; 1/2 HP for larger or deeper pits) and the discharge pipe size (typically 1.5 or 2 inches). Disconnect the old pump (unscrew the discharge coupling, unplug, lift out). Lower the new pump into the pit, connect the discharge coupling with a hose clamp, plug in, and test by pouring water into the pit to trigger the float.
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