Sump pump not working? Test it in 2 minutes, fix it in 30

A sump pump is the one appliance in your house that fails exactly when you need it most — during the storm that fills the pit. Test it before the storm, not during. Here's the two-minute test, the four things that go wrong, and the honest line between fixing it and replacing it.

The 2-minute bucket test

Pour a 5-gallon bucket of water into the pit. The float should rise, the pump should kick on, the water level should drop fast, and the pump should shut off within a few seconds of the pit emptying. Then listen at the discharge pipe outside — water should come out, and when the pump stops you should hear a single clunk from the check valve.

Do this twice a year. Put it on your seasonal checklist.

Symptom → cause

| What's happening | Likely cause | Fix | DIY cost | |---|---|---|---| | Totally silent, won't start | Tripped breaker or GFCI, unplugged, dead motor | Reset; test outlet with a lamp | $0 | | Silent, outlet is live | Float stuck against the pit wall or debris | Free the float, reposition the pump | $0 | | Hums but doesn't pump | Jammed impeller or seized motor | Clear debris from intake; replace if seized | $0–$200 | | Runs, pit doesn't drain | Clogged intake screen, frozen or blocked discharge line, failed check valve | Clear screen; thaw/clear line; replace check valve | $0–$30 | | Runs constantly | Float stuck "up," check valve letting water fall back, pump undersized, or pit genuinely filling that fast | Free float; replace check valve; upsize pump | $0–$250 | | Short-cycles on and off every few seconds | Check valve missing or failed, float range set too narrow | Install/replace check valve; adjust float tether | $15–$30 | | Loud grinding or rattling | Worn bearings or impeller hitting debris | Clear debris; if noise persists, replace | $0–$250 |

The four fixes, in order

1. Power. Sump pumps are usually on a GFCI outlet, and GFCIs trip. Press reset. Check the breaker. Plug a lamp into the outlet. Thirty seconds, solves a quarter of "dead" pumps.

2. The float. Unplug the pump first. Look in the pit. Vertical floats ride a rod and can jam on it; tethered floats hang on a cord and get wedged between the pump and the pit wall. Free it, then make sure the pump sits in the center of the pit with the float clear on all sides. A pit that's too small for a tethered float is a common cause of a brand-new pump "failing."

3. The check valve. The vertical pipe leaving the pump has a one-way valve, usually a black rubber or PVC fitting with hose clamps. When it fails, every gallon the pump pushes up falls back down, so the pump runs forever or short-cycles. Replacement is $15–$30 and two hose clamps. Install it with the arrow pointing up — people get this wrong.

4. The intake and discharge. Unplug the pump, lift it out, and check the screen at the bottom for gravel, sediment, or a dead mouse. Outside, make sure the discharge pipe isn't crushed, buried under mulch, or frozen solid at the outlet in winter. A frozen discharge line is the number-one cold-weather failure; a freeze-relief fitting ($20) on the line prevents it.

Replace it if

• It's 7 to 10 years old. That's the service life. A pump that's "still working" at year 10 is a pump that fails during the next big storm.
• The motor hums but won't spin after you've cleared the impeller.
• It runs but moves noticeably less water than it used to.
• The housing is corroded or the cord is damaged.

A good 1/3 or 1/2 HP cast-iron submersible is $150–$300. Swapping it is 30 to 60 minutes: unplug, unscrew or cut the discharge pipe above the check valve, lift out the old pump, set the new one, reconnect with a rubber coupling, plug in, bucket test. The one thing to get right is matching the discharge pipe diameter (usually 1-1/2 inch).

Get a battery backup. Seriously.

The storm that floods the basement is the storm that knocks out power. A battery-backup pump sits in the same pit and runs 6–12 hours on a deep-cycle battery. $250–$500 for the kit, $150–$250 for the battery, an afternoon to install. Or a water-powered backup ($200–$400) that runs off municipal water pressure with no battery at all. Either one is cheaper than one insurance deductible.

When to call a pro

• The pit is overflowing right now and the fixes above didn't work. Call an emergency plumber; this is what they're for.
• You're replacing the pump and the pit is undersized, has no check valve, or the discharge plumbing is a mess of mismatched fittings. A plumber reworks all of it at once, $600–$1,200 installed with a quality pump, and it stops being a recurring problem.
• The pump works but the basement still gets water. That's not a pump problem — see water in the basement after rain.
• You want a backup system and a hard-wired alarm and would rather it be done once, right.

Any of those, and the Find a Pro page will get you a couple of plumbers' quotes in a day. Compare the quote against $300 in parts and an hour in the cost planner — for a straight pump swap, DIY wins; for a pit rework, the plumber usually does.