Sump Pump Not Working? 8 Causes and How to Fix Each One (2026)
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Your sump pump isn’t working. Water is rising in your pit, or the pump is running but doing nothing, or it’s completely silent when it should be on. Every minute matters.
Need a fix today? If water flows back into the pit after every cycle, the likely culprit is the check valve — a cheap part fix. Our pick is the Zoeller 30-0181 check valve. If the pump won’t kick on while water rises, a stuck float switch is the next suspect — pumps with a plug-in piggyback switch can take a PumpSpy 10 ft vertical replacement float switch. If a quick troubleshoot doesn’t solve it, our top-rated replacement pick, the Zoeller M53, installs in under an hour so you’re not stuck bailing water by hand.
If it turns out your pump is simply dead, skip ahead to our top replacement pick: Zoeller M53 →
This guide covers every reason a sump pump stops working and gives you a fast diagnostic path to fix it — starting with the most common causes and ending with when to call a plumber or replace the pump entirely.
Step 1: Check Power First (2 Minutes)
Before anything else, verify the pump has power. A tripped breaker or unplugged cord is one of the most common causes:
- Is the pump plugged in? Check the outlet — the plug sometimes pulls loose, especially if the cord was tugged during maintenance.
- Is the GFCI tripped? Sump pumps must be on a GFCI circuit. Find the GFCI outlet (it may be on a different wall or even in an adjacent space) and press the Reset button.
- Check the circuit breaker. A tripped breaker looks “in between” — not fully on, not fully off. Flip it fully off, then back on.
- Is there power at the outlet? Plug a lamp or phone charger into the same outlet. If it doesn’t work, the outlet is the problem — not the pump.
Sump Pump Not Working: 8 Causes and Fixes
1. Float Switch Stuck or Tangled
Symptoms: Pump doesn’t turn on even with water in the pit; or pump runs continuously without stopping.
What happens: The float switch is a bobber that rises with water level and triggers the pump. In a narrow pit, the float can press against the pit wall or the pump cord and get stuck — either preventing the pump from activating, or holding it on when the water level drops.
Fix: Reach into the pit and manually lift and lower the float. It should move freely. If it’s caught on the cord, reposition the cord so it hangs away from the float path. Many homeowners add a zip tie or cord clip to keep the power cord against the pump body.
2. Pump Is Running But Not Pumping Water
Symptoms: You can hear the motor humming, but the water level isn’t dropping.
What happens: The most common cause is a clogged or frozen discharge line. Water has nowhere to go, so the pump runs but can’t move anything. A second cause is a failed or backwards-installed check valve that prevents outflow.
Fix: Disconnect the discharge line at the pump outlet and verify water flows freely when the pump runs. If it does, the clog is further up the line. If nothing comes out, the impeller may be jammed with debris — turn off the pump, remove it, and clean the impeller housing. For frozen discharge lines, see our guide on discharge line freezing fixes.
3. Clogged Inlet Screen or Impeller
Symptoms: Pump runs but moves very little water; unusual noise (grinding, rattling).
What happens: Sump pits accumulate gravel, silt, and debris over time. The pump’s inlet screen or the impeller itself gets clogged, reducing flow dramatically.
Fix: Unplug the pump, remove it from the pit, and rinse it with a garden hose. Most submersible pumps allow you to unscrew the bottom housing to access and clean the impeller. While the pump is out, also clean the pit of accumulated sediment — this is annual maintenance that prevents future clogs.
4. Check Valve Installed Backwards or Failed
Symptoms: Pump runs constantly; water drains back into pit immediately after pump shuts off; loud bang or “water hammer” when pump cycles off.
What happens: A check valve is a one-way valve that prevents water from flowing back down the discharge line into the pit when the pump shuts off. If it’s installed backwards or the flapper has failed, discharged water flows straight back in, causing the pump to run continuously in a pointless loop.
Fix: Inspect the check valve’s directional arrow — it must point away from the pump (toward discharge). If installed correctly but still failing, replace it. Check valves are $15–$40 and take 15 minutes to swap.
5. Pump Overheated and Tripped Thermal Overload
Symptoms: Pump was running fine, stopped suddenly, and now won’t restart. No obvious power issue.
What happens: Most sump pumps have a thermal overload protector that shuts the motor down if it overheats. This happens when the pump runs dry (water level drops too low), runs continuously for extended periods, or the motor is nearing end of life.
Fix: Wait 20–30 minutes for the pump to cool, then try restarting. If it runs again, the thermal protector did its job. If it keeps tripping, the pump may be undersized for your water volume, or the motor is failing. Check if the pump is running dry by verifying there’s water in the pit when it’s operating.
6. Failed Float Switch
Symptoms: Pump won’t turn on at all; manually lifting the float doesn’t help; pump works if you bypass the float.
Fix: Test the float switch by bypassing it temporarily. On most submersible pumps, the float switch cord plugs into the motor cord with a piggyback plug. Plug the motor cord directly into the outlet (bypassing the float). If the pump runs, the float switch is failed and needs replacement. Float switch replacements cost $15–$35 and are pump-model-specific.
7. Discharge Line Frozen or Blocked
Symptoms: Pump runs but water level doesn’t drop; happens during winter or after first cold snap.
Fix: Check the outdoor discharge line exit point. If it’s iced over, carefully thaw it with warm (not boiling) water. As a permanent fix, install a freeze protection outlet cover with a weep hole that allows drainage even if the line freezes. See our full guide on sump pump discharge line freezing.
8. Motor Burned Out
Symptoms: Pump is completely silent; GFCI and breaker are fine; bypassing the float still produces nothing; pump smells like burning.
Fix: At this point, the pump needs to be replaced. A burned-out motor is not economically repairable. Most residential sump pumps last 7–10 years; if yours is in that range, a new pump is the right call regardless.
Quick Diagnostic Chart
| Symptom | Most Likely Cause | Fix |
|---|---|---|
| Pump is completely silent | No power / GFCI tripped | Check outlet, GFCI, breaker |
| Pump hums but doesn’t pump | Clogged impeller or frozen discharge | Clean impeller; thaw/clear discharge line |
| Pump runs continuously | Float stuck on; check valve failed | Reposition float; replace check valve |
| Pump won’t turn on (power is fine) | Float switch failed | Bypass test; replace float switch |
| Pump started then stopped suddenly | Thermal overload tripped | Let cool 20–30 min; restart |
| Water drains back after pump stops | Check valve backwards or failed | Inspect arrow direction; replace if needed |
| Pump is silent and smells burnt | Motor burned out | Replace pump |
When to Replace Instead of Repair
Repair vs. replace comes down to age and cost. If the pump is under 5 years old and the problem is a float switch ($25) or check valve ($20), repair makes sense. If the pump is 7+ years old or the repair involves the motor itself, replacement is the better investment.
New residential sump pumps start at $150–$250 for quality units (Zoeller M53, Wayne CDU980E). The labor to install a new pump is the same as the labor to diagnose and attempt a complex repair.
When to Call a Plumber
Call a professional if:
- You’ve worked through this diagnostic list and the pump still doesn’t work
- There’s active flooding and the pump isn’t keeping up
- You need the GFCI circuit rewired or a new dedicated circuit run
- The pit liner or discharge line needs replacement — not just the pump
For everything else — float switch replacement, check valve swap, impeller cleaning, pump replacement — these are straightforward DIY tasks that most homeowners can handle in under an hour.
Photo credit: Famartin, Wikimedia Commons, CC BY-SA 4.0.
