Sump pump running constantly
A sump pump that never stops running will burn out its motor in weeks and drive up your electric bill. Common causes: stuck float, missing check valve, or genuinely high water table needing a bigger pump.
Quick answer
Turn off power to the sump pump. Watch the water level in the pit. If it drops to normal and stays there, the float switch was stuck (fixable). If water keeps rising, you have a genuine drainage issue: check the check valve first (missing or broken lets water flow back in). If the check valve is fine, groundwater is exceeding pump capacity — need larger pump, better exterior drainage, or interior French drain.
Key facts
| Difficulty | Medium |
|---|---|
| Time | 30–90 min |
| Parts cost | $0–$100 |
| Tools needed | Flashlight, screwdriver, bucket |
| Parts needed | Check valve ($10–$20), possibly a new pump |
What's happening
A properly working sump pump has clear cycles: water rises → pump runs → pit empties → pump stops → wait for water to rise again. Normal cycle time varies from minutes (heavy rain, high water table) to days (dry conditions).
Constant running has three main root causes: the pump can't sense the pit is empty (stuck float), water keeps flowing back into the pit (bad check valve), or genuine water inflow exceeds pump capacity (needs bigger pump or better drainage).
The distinction matters — a stuck float is a 5-minute fix; genuine capacity issues are a $2,000+ investigation.
Common causes (ranked by frequency)
- Missing or failed check valve 35% of cases
The check valve prevents water from flowing back down into the pit after the pump stops. Without it, water in the vertical discharge pipe flows back — pump immediately runs again.
- Float switch stuck in ON position 25% of cases
Float caught on pit wall, pump body, or debris. Pump thinks water level is high even when pit is empty.
- High water table / heavy rain 20% of cases
Groundwater actually is coming in continuously. Normal during heavy storms but concerning if constant during dry weather.
- Pump undersized for load 10% of cases
Small pump can't keep up. Water pours in faster than the pump can move it out — pump never gets ahead.
- Broken supply line or plumbing leak into pit 10% of cases
A leaking pipe or broken interior drain tile is dumping water into the pit constantly.
How to diagnose
Step 1 — turn off the pump temporarily. Unplug it. Watch the pit for 30 minutes.
- Water level drops or stays same: Float switch stuck. Water wasn't actually accumulating — pump was cycling on empty. Fix the float.
- Water rises visibly in 30 minutes: Real water inflow. Continue diagnosis.
Step 2 — check the check valve. Look at the discharge pipe above the pump. There should be a check valve (small dome-shaped fitting) within 12" of the pump. If missing or the flap inside is jammed, water flows backward when the pump stops. Test: run the pump manually briefly, then listen for water flowing back into the pit after it stops. Backflow = bad check valve.
Step 3 — investigate water source (if inflow is real and check valve is fine):
- Just had heavy rain? Wait 24 hours after the storm ends — inflow should slow dramatically.
- Constant inflow during dry weather? Likely broken drain tile, high water table, or plumbing leak.
- Water is warm or has soap/chemicals? Interior plumbing leak — trace source.
The fixes
Free the stuck float TRY FIRST
Tools
- Flashlight
Parts
- None
- Unplug the pump for safety.
- Look into the pit — is the float physically caught on something? Common: caught between pit wall and pump, tangled in cord, or resting on debris.
- Free the float so it can rise and fall unimpeded across its full range.
- Clean debris from the pit — small stones, silt, roots that may be catching the float.
- Reposition the pump if needed so the float has clear travel.
Install or replace the check valve IF WATER FLOWS BACK
Tools
- Adjustable wrench
- PVC saw or utility knife (for glued joints)
Parts
- Check valve ($10–$20)
- Threaded couplings if converting
- Unplug the pump.
- Cut into or unscrew the discharge line above the pump — position for the check valve.
- Install the check valve with the arrow pointing UP (direction of water flow).
- Best practice: use rubber unions on both sides of the valve for easy future removal.
- Position within 12" of the pump — closer is better.
- Plug pump back in.
Address genuine inflow issues IF WATER SOURCE IS THE PROBLEM
Tools
- Time and possibly professional consultation
Parts
- Variable — could range from downspout extensions to full waterproofing
- Address exterior drainage first — cheapest interventions: Extend downspouts 6+ feet from foundation. Regrade soil to slope away.
- Check for foundation cracks that may be admitting water. Small ones can be sealed with polyurethane injection.
- Consider a larger pump if consistent overwhelming — 1/2 HP or even 3/4 HP for very high water tables.
- For truly extreme cases, interior French drain (drain tile around basement perimeter feeding to sump pit) is the pro solution — $3,000–$8,000.
- Exterior waterproofing (excavation and membrane) is the most complete fix — $8,000–$20,000.
Prevention
Prevent constant-running problems:
- Include a check valve at initial install — often skipped by budget installers.
- Keep the sump pit clean — sweep debris every 6 months.
- Address exterior drainage issues before installing bigger and bigger pumps.
- Test pump quarterly with bucket — verify normal cycle behavior.
- Consider a smart WiFi sump monitor — alerts you to excessive cycling early.
When to call a pro
- Water inflow overwhelming even after check valve and float fixes
- You suspect a broken underground drain tile or foundation crack
- Interior French drain installation is being considered
- Recurring flooding despite multiple pump upgrades
- You need a professional water source assessment
Costs: Basement waterproofing assessment: $150–$300. Interior French drain: $3,000–$8,000. Exterior waterproofing: $8,000–$20,000. Battery backup pump added: $400–$800.
Cost estimate
Frequently asked questions
Varies wildly by conditions. Dry weather: hours or days between cycles. Heavy rain: every few minutes is normal. Constant cycling during dry weather = problem.
Yes. Sump pump motors are designed for intermittent duty. Continuous running causes overheating and shortens life dramatically — sometimes to weeks instead of years.
During and immediately after heavy rain — yes, expected. If it runs constantly for many hours after rain has stopped, that's a check valve or drainage problem.
Only if genuine inflow exceeds current pump capacity. Bigger pump doesn't fix a stuck float or missing check valve. Diagnose the actual issue first.