How to test a sump pump, and how often

Why a pump that worked last spring can fail tonight

A sump pump spends most of its life doing nothing, and that is when the failures set up: silt settles around the intake and the float, iron bacteria glue the switch to the pit wall, the flapper in the check valve stiffens open, and the discharge outlet outside fills with leaves or freezes. None of it makes a sound. The pump looks fine from the top of the pit right up to the first night it has to run for six hours straight.

When we opened pits on flooded-basement calls, the pump itself was rarely the first thing that had failed. Far more often it was the switch, the check valve, a tripped outlet or a crushed discharge line, and every one of those would have shown up in a five-minute test the weekend before. The manuals agree: Zoeller's installation instructions say to inspect and test the system at least every three months, and Wayne's say to inspect three to four times a year and to pour a bucket of water into the pit to confirm the pump starts. Our schedule is tighter, because we have seen what a missed quarter costs: five minutes every month, a longer look each spring and fall, and a test before any storm in the forecast.

What you are testing

A sump system is five parts, and water meets them in this order: the pit and the drain tile that feeds it, the pump, the switch that starts it, the check valve on the riser that keeps pumped water from falling back, and the discharge line that carries water outside and away. The test walks the same path. Water goes in, the switch should notice, the pump should move it, the valve should hold it, and it should come out of the pipe in the yard. If a link breaks, you want to know which one; a stuck float and a seized motor have very different fixes.

Tools and materials

You need almost nothing, which is the point: the test should be easy enough that you actually do it.

• A garden hose that reaches the pit, or a 5-gallon bucket (an 18-in. pit rises only about an inch per gallon, so a hose is easier)
• A flashlight or headlamp
• Nitrile gloves; sump water is not clean
• A phone to time the pump-down and photograph the pit
• A stiff wire for the weep hole
• Optional: a cup of water for the high-water alarm probe, painter's tape and a marker for the log

Testing the battery backup

Most current controllers run a weekly self-test, which proves the circuit works. It does not prove the pump can lift water through its own check valve or that the float is set where it should be. Once a month, after the primary test:

1. Unplug the primary. Leave the backup's charger plugged in.
2. Fill the pit past the primary's turn-on level. Nothing should happen yet; the backup's float belongs 2 to 3 in. higher. If the backup starts at the same level as the primary, it has been running on every cycle and wearing out its battery; reset the float height.
3. Keep filling until the backup starts. It should pump the pit down, the controller should alarm, and a Wi-Fi unit should alert your phone. Water should not run back down its own riser when it stops; the backup needs its own check valve.
4. Plug the primary back in, silence the alarm, and confirm the charger returns to charging within a few minutes.
5. Look at the battery. Check the install date on the case; deep-cycle batteries last three to five years whether or not they ever run a storm. Terminals clean and tight. Wet-cell batteries get distilled water with the charger off; AGM has nothing to open. A bulging case or a fault light means it is done.

For a water-powered backup, lift its float by hand with the primary unplugged. The supply valve should open, the ejector should pull water from the pit and the water meter should spin. Check that the backflow preventer is in place and dry. These units use roughly a gallon of city water for every two they pump, so keep the test short.

If there is no backup, the monthly test is the time to think about it. A primary that passes every test still stops when the power does, and the storms that fill pits take lines down. Our battery backup roundup and install guide cover the choice and the afternoon's work.

The seasonal checks

The monthly test catches the pump. The slower failures live outside the pit.

Spring. Walk the discharge from the rim joist to its end: sagging runs that hold water, pulled joints, a buried line you cannot see the end of (run the pump and find where water surfaces). Clear the outlet. Inside, confirm the lid seals and the drain tile inlets into the pit are flowing, not silted shut.

Fall. Same walk, plus freeze protection: slope along the whole discharge so water cannot sit and freeze, a freeze-relief fitting near the rim joist so the pump has somewhere to push water if the line beyond it ices over, and an outlet the plow or the roof slide will not bury. Run the backup through two pit-downs in a row with the primary unplugged; replace its battery if it is in its fourth year.

Once a year, clean the pit. Unplug, pump down, lift the pump out onto cardboard. Scoop and wet-vac the silt, rinse the intake screen and float, clear the weep hole, turn the impeller by hand with the power off, set it back level, and run the full test. Wayne's manual says to replace a tethered switch every two years; the same logic applies to any switch that hesitated during a monthly test.

What a failed test looks like, and what it means

Float at the top, nothing happens. Switch, outlet or motor, in that order. Bypass the piggyback switch, test the GFCI, then suspect the pump. A tethered float wedged against the pit wall is a stuck switch, not a dead pump; reposition it and shorten the tether.

Hums but moves no water. Unplug it. The impeller is jammed with grit, or the pump has air-locked because the weep hole is clogged or missing. Clear the hole; if that is not it, pull the pump and turn the impeller by hand.

Pumps, stops, and the pit refills in seconds. The check valve is not holding. Replace it; until you do, the pump does two or three times the work it should.

Will not shut off. The float is hung up or the switch contacts have welded. Unplug it before you reach in. If the float moves freely and it still runs, replace the switch; if the level never drops while it runs, read the running constantly guide, because the problem may be the discharge.

Slow. A pump-down that took 15 seconds and now takes 45 is a worn impeller, a blocked intake, a bellied discharge full of silt or a check valve that only half opens. Clean first, then compare.

Trips the breaker or GFCI. Once could be the outlet. Twice is water in the motor or a failing winding; replace the pump before the next storm rather than reset it again.

Oil on the water, rust streaks from the seal. The motor seal has gone and water is next.

Any pump that fails a test and is more than seven or eight years old is cheaper to replace than to coax along. Our replacement guide walks the swap and the sump pump roundup has the pumps we would put in. The M53 below is the one we found most often still running in pits older than its warranty.

When to call a pro

Call a plumber or basement waterproofer if the pump trips the breaker more than once, if the pit holds water above the turn-on level while the pump runs (the discharge may be blocked or frozen underground), if the discharge line is buried and you cannot find where it comes out, if the outlet or the electrical panel sits where a pit overflow would reach, or if the pit is a hole in the slab with no liner and no lid. A plumber replaces a pump in an hour or two; a waterproofer handles the pit, drain tile and discharge problems a new pump cannot fix. If water has already come over the rim onto a finished floor, the first 24 to 48 hours decide whether it is a cleanup or a mold job, and our 72-hour guide is where to start. The form below reaches vetted local plumbers and waterproofers through HelpMeNow.com.