Sump pump not turning on
A sump pump that won't run when water is rising is a basement flood in progress. Quick diagnostics: power, float switch, impeller, then replacement. If water is imminent, use a wet-vac while diagnosing.
Quick answer
If water is rising: (1) confirm power at the breaker and GFCI outlet, (2) pour a bucket of water into the sump pit to test the float switch, (3) if float is stuck, gently free it, (4) if pump is silent even with float lifted, motor has failed — replace. If water is imminent, use a wet-vac for emergency removal while you diagnose. A backup sump pump (battery or water-powered) prevents this scenario.
Key facts
| Difficulty | Medium |
|---|---|
| Time | 15–60 min |
| Parts cost | $0–$300 |
| Tools needed | Flashlight, multimeter (optional), bucket, wet-vac (if flooding) |
| Parts needed | New sump pump ($150–$400) if replacement needed |
What's happening
A sump pump sits in a pit at the lowest point of your basement. When groundwater rises into the pit, a float switch (mechanical or tethered) triggers the pump motor, which then spins an impeller that pushes water out through a discharge pipe to outside the house.
Any link in this chain can fail: power outage, tripped GFCI, stuck float, jammed impeller, failed motor. Because sump pumps often sit unused for months at a time (dry season), then are expected to run reliably during heavy rain, undetected failures are common.
The rule: Test your sump pump quarterly by pouring a 5-gallon bucket of water into the pit. Better to discover a failure during testing than during a storm.
Common causes (ranked by frequency)
- Power lost (unplugged / breaker tripped / GFCI tripped) 35% of cases
Sump pumps are often on GFCI circuits that can trip from moisture or nuisance faults. Also frequently unplugged accidentally.
- Float switch stuck 30% of cases
Debris in the sump pit, sediment buildup, or the switch itself getting caught on the pit wall. Pump can't sense high water.
- Motor failed 20% of cases
After 7–10 years of use, motors wear out. May hum without spinning, or be completely silent. Requires pump replacement.
- Impeller jammed 10% of cases
Small stones, coins, or debris in the sump pit lodged in the impeller. Motor may hum but pump can't move water.
- Discharge pipe blocked or frozen 5% of cases
In winter, the exterior discharge can freeze. Pump runs but water can't leave, eventually overflowing the pit.
How to diagnose
If flooding is imminent: Get a wet-vac or portable pump moving water manually FIRST. Then diagnose.
Step 1 — verify power: Is the pump plugged in? Is the breaker on? Is the GFCI outlet tripped (little red button)? Reset if tripped and see if pump kicks on.
Step 2 — test the float switch: Pour a 5-gallon bucket of water into the sump pit. The float should rise, triggering the pump. If pump doesn't start, either float switch is stuck or motor is dead.
Step 3 — check float physically: Look into the pit. Is the float caught on the pump or pit wall? Free it if so.
Step 4 — bypass the float: With water in pit, lift the float manually. If pump runs when you lift it, the float switch itself is bad ($15 part, though many pumps require full replacement). If pump still doesn't run, motor is dead.
Step 5 — listen for humming: If motor hums but nothing happens, impeller is jammed. Turn off power, remove pump, inspect impeller.
The fixes
Reset power and float TRY FIRST
Tools
- Flashlight
Parts
- None
- Confirm the pump is plugged in. Vibration can loosen plugs over time.
- Reset the GFCI outlet if tripped — press the RESET button.
- Check the breaker — if tripped, turn fully OFF then back ON.
- Look into the sump pit with a flashlight. Is the float caught on debris or the pit wall? Free it gently.
- Pour a 5-gallon bucket of water into the pit to test if the pump activates.
Clear jammed impeller IF MOTOR HUMS BUT NO WATER MOVES
Tools
- Screwdriver
- Rubber gloves
Parts
- None (unless replacement needed)
- Turn OFF power at the breaker. Do not attempt to work on the pump while it's plugged in.
- Disconnect the discharge pipe union (large coupling above pump).
- Lift the pump out of the pit. Water in the pit is fine as long as power is off.
- Turn the pump upside down and look at the impeller intake underneath.
- Clear any debris — small stones, coins, gravel are common culprits. Use a screwdriver to gently free anything jammed.
- Spin the impeller by hand — should turn freely.
- Reinstall the pump, reconnect discharge, restore power. Test with bucket of water.
Replace the pump IF MOTOR IS DEAD
Tools
- Screwdriver
- Adjustable wrench
- PVC saw (if hard-piped)
Parts
- New sump pump ($150–$400)
- PVC couplings or check valve if needed
- Turn OFF power at the breaker.
- Disconnect discharge pipe. Union or PVC cut.
- Lift old pump out.
- Note the discharge pipe height, pump position, cord routing. New pump should match.
- Match pump specs: 1/3 HP is standard for most homes; 1/2 HP for high water tables. Cast iron lasts longer than plastic.
- Install new pump in pit, making sure the float has full range of motion.
- Connect discharge with new check valve to prevent backflow ($10 part, essential).
- Plug in and test with bucket.
Prevention
Sump pump reliability practices:
- Test quarterly — pour a 5-gallon bucket into the pit and verify pump runs.
- Install a battery backup pump — $200–$500 for the second pump; runs when power is out during storms (when you need it most).
- Replace primary pump every 7–10 years as preventive maintenance — don't wait for failure.
- Add a water alarm in the pit ($15) — alerts you if water rises too high, before flooding damage.
- Insulate the exterior discharge in freeze-prone climates to prevent frozen discharge lines.
- Consider a smart WiFi sump pump monitor ($50–$150) — alerts you on your phone if the pump fails or activates unusually often.
When to call a pro
- Active flooding you can't manage with a wet-vac
- Sump pit is deep or awkwardly located and you can't reach the pump safely
- Water level has risen above the pump — electrocution risk
- You suspect the discharge pipe is broken underground
- Repeated pump failures despite replacement (indicates high water table needing more capacity)
Plumber cost: $250–$500 for pump replacement (labor + pump). Battery backup pump install: $400–$800. Emergency after-hours service: 1.5–2x rate.
Cost estimate
Frequently asked questions
7–10 years for average use; less for pumps that run frequently. Consider proactive replacement at year 8, especially before a wet season. A pump that runs several times a day wears out faster than one that runs occasionally.
Yes — most severe storms cause power outages. A primary sump pump without backup is a coin flip during exactly the situations you need it. Battery backup adds $200–$500 upfront; flood damage averages $10,000–$30,000.
For emergency temporary drainage — yes. Won't have automatic float control, and you'll need to monitor. Not a long-term solution.
Groundwater seeping in — often the pump is doing its job perfectly. But if it runs constantly (every few minutes), see sump pump running constantly. Could indicate high water table, broken supply line into pit, or a stuck float.