Short answer: Bob Vila lists the main reasons a sump pump stops working: no power (unplugged, dead outlet, tripped breaker), a stuck float switch, a clogged intake screen or impeller, a check valve installed backward or stuck, a blocked discharge line, or a burned-out motor. Test it by pouring a bucket of water into the pit. If it hums but does not pump, or does not start at all after you confirm power, it likely needs repair or replacement.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| Nothing happens when the pit fills | No power or failed switch | Test the outlet; check the breaker | If power is fine |
| Starts when you lift the float by hand | Float switch stuck | Clear whatever jams the float | Rarely |
| Hums but does not move water | Clogged impeller or intake, or failed motor | Unplug; clean the intake screen | Often |
| Runs but water comes back | Check valve stuck or installed backward | Check the arrow on the valve | Often |
| Pump is 7 to 10+ years old | Worn-out motor | Plan a replacement | Yes |
Test it
- Make sure the pump is plugged directly into a working outlet (not a long-term extension cord) and the breaker is on.
- Slowly pour a bucket of water into the pit.
- Watch the float rise and the pump start. It should empty the pit and stop.
- If it does not start, unplug it and lift the float by hand after plugging back in, to see if the float is the problem.
Clean it
Unplug the pump, lift it out if possible, and clear debris from the intake screen and impeller. Check that the discharge pipe outside is not blocked or frozen.
Be ready for the next storm
- HomeGuide suggests testing every three months, and monthly in the rainy season.
- A battery backup pump keeps working during a power outage, when storms often hit.
- Keep a spare float switch or know a plumber who can come quickly.
When to call a professional
- The pump will not start with power confirmed and the float free.
- The motor hums, overheats or trips the breaker.
- The pump is old or water is already rising in the basement.
What it usually costs
HomeGuide (2026) lists sump pump repairs at about $200 to $870 and a replacement pump at about $400 to $700 on average. Battery backup systems add to that cost.
Frequently asked questions
How do I know if my sump pump is bad?
If it does not start when you fill the pit with water, runs but does not lower the water, or makes grinding noises, it may be failing.
How long do sump pumps last?
HomeGuide and Bob Vila put the average at about 7 to 10 years.
Related problems
- Sump pump running constantly
- Water in basement after rain
- Outlet not working
- GFCI outlet won’t reset
- Flooded basement
Sources
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.