Sump Pump Failed and the Basement Is Flooding: Step-by-Step

If your sump pump fails and the basement floods, check for electrical danger before going down the stairs. Then find out why the pump stopped (power, float switch, check valve or overload), get the water moving out with a backup or rental pump, photograph the damage, and start drying within 24 to 48 hours to limit mold.

By West Chester Flood Cleanup Editorial Team · Published 2026-11-05

A sump pump usually fails at the worst time: in a heavy rain, when the groundwater around your foundation is highest. Here is what to do, in order.

Is it safe to go downstairs?

Before you step into a flooded basement, answer these questions.

• Is the water touching anything electrical? Outlets, power strips, extension cords, a furnace, a water heater, a freezer or the sump pump cord itself. If yes, don't go in.
• Can you shut off power without walking through water? If the electrical panel is upstairs or in a dry spot, turn off the breakers for the basement. If the panel is in the basement and you would have to wade to it, call your electric utility or an electrician.
• Do you smell gas? Floodwater can move or damage gas appliances. If you smell gas, get everyone out and call the gas company from outside.
• Is the water clean? Groundwater from a sump pit is usually clean when it first enters. If a floor drain is backing up, or the water smells like sewage, treat it as contaminated and read our guide to sewage backup cleanup.

Wear rubber boots and gloves. Never use a regular household vacuum on standing water.

Common causes of sump pump failure

Knowing why the pump stopped tells you whether you can get it running again tonight.

Power loss

The most common cause. Heavy storms knock out power exactly when the pump is needed. A tripped GFCI outlet or breaker can also cut power without anyone noticing. Check the outlet and the breaker panel first.

Stuck or failed float switch

The float tells the pump when to turn on. It can get jammed against the side of the pit, tangled in the cord or stuck by debris. With power off, look in the pit. If the float is wedged, freeing it may restart the pump. Vertical and tethered floats both wear out over time.

Failed check valve

The check valve on the discharge pipe stops pumped water from falling back into the pit. If it fails, the pump runs constantly, pumping the same water in a loop, and can burn out. A pump that hums or cycles fast but doesn't lower the water often points here.

Overload or undersized pump

In a long, heavy rain, more water can enter the pit than a small pump can move. The pump runs nonstop, overheats and may shut off on thermal protection. This is common in basements on low ground, near streams or with high water tables.

Frozen or blocked discharge line

In winter, the outdoor discharge pipe can freeze. In any season, it can be crushed or clogged with leaves. If the pump runs but no water comes out outside, check the discharge line.

Old age

Many sump pumps wear out within several years, sooner if they run often. If yours is old and you don't know when it was last tested, assume it's near the end of its life.

Temporary pumping

Once it's safe, the goal is to get water moving out of the house.

• Restart the pump if the problem was a tripped breaker or a stuck float.
• Use a backup. If you have a battery or water-powered backup pump, make sure it's running.
• Rent or buy a utility pump. Hardware stores and rental shops carry submersible utility pumps that run on a regular outlet. Run the discharge hose outside, well away from the foundation and downhill.
• Use a generator safely. If the power is out, run a portable generator outside only, far from doors and windows, to avoid carbon monoxide. Never run it in a garage or basement.
• Wet-vac shallow water once the pit is under control.

Don't pump a basement out too fast if water outside is still very high. Groundwater pressure against a foundation wall can, in rare cases, damage the wall if the inside is emptied all at once. If water is coming through the walls from a creek or surface flooding, wait for levels outside to drop.

Drying after the water is gone

Removing the water is about half of the job. Concrete, block walls, framing, drywall and carpet keep holding moisture after the floor looks dry.

1. Move wet contents out. Boxes, rugs, furniture and stored items should go to a dry area or outside. Cardboard and paper soak up water and can start growing mold quickly.
2. Pull wet carpet and pad. In most flooded basements, pad can't be saved. Carpet sometimes can, if the water was clean and drying starts fast.
3. Check finished walls. Drywall wicks water upward. If it got wet, the bottom of the wall may need to be cut out so the cavity can dry.
4. Run dehumidifiers, not just fans. A basement is a closed space. Without dehumidification, moisture just moves around.
5. Measure. Moisture meters show when materials are actually dry. Feeling the surface isn't enough.

The EPA says mold can start growing on damp materials within 24 to 48 hours. A basement that stays damp for a week will almost always have a mold problem. Our basement flooding service covers extraction, drying and moisture readings for finished and unfinished basements.

Insurance: why sump coverage is often a separate endorsement

Many homeowners are surprised to find that a standard Pennsylvania homeowners policy may not cover water that backs up through a sump or drain. The Commonwealth's flood insurance guidance notes that sewer and sump-pump backup usually needs a separate endorsement, and flood (surface water from outside) is excluded from standard homeowners policies (pa.gov flood insurance).

What that means in practice:

• With a water backup endorsement: damage caused when the pump fails or can't keep up may be covered, up to the endorsement limit. Limits are often modest, so check the number.
• Without one: the claim may be denied even though the water entered through your own pit.
• If a creek or surface flooding came in: that's usually flood, covered only by a separate flood policy.

Call your agent, describe exactly what happened and ask which coverage applies. Our guide on whether homeowners insurance covers water damage in Pennsylvania explains the differences in more detail.

Preventing a repeat

Once the basement is dry, make sure this doesn't happen again.

• Add a battery backup pump. It sits in the same pit and takes over when power fails or the main pump can't keep up. Check and replace the battery on the maker's schedule.
• Consider a water-powered backup if you have municipal water pressure. It needs no battery, but uses house water to run.
• Install a high-water alarm. A cheap alarm or a Wi-Fi sensor in the pit alerts you before water reaches the floor.
• Test the pump every few months. Pour a bucket of water into the pit and watch it cycle.
• Replace an aging pump on your schedule, not during a storm.
• Fix the discharge. Make sure water exits well away from the foundation and can't freeze.
• Prepare before big rains. Our storm prep checklist covers the 48 hours before heavy rain.

Basements in low-lying neighborhoods of West Goshen and around the area's smaller creeks see this often after heavy rain. See our West Goshen page for local service details.

FAQ

How long can a basement sit wet before mold grows?

The EPA's guidance is that mold can start within 24 to 48 hours on damp materials. Concrete itself doesn't feed mold, but drywall, wood, carpet, boxes and dust do.

Can I run my sump pump on a generator?

Yes, if the generator is sized for the pump's starting load and runs outdoors. Plug the pump directly into the generator with a heavy-duty outdoor cord, or have an electrician install a transfer switch.

Will a new sump pump stop all basement flooding?

No. A sump pump handles groundwater under and around the slab. It won't stop a creek flood, a sewer backup or water coming through walls from poor grading.

Do I need to throw out everything that got wet?

Not always. Hard items can usually be cleaned. Porous items like carpet pad, cardboard and mattresses are usually discarded, especially if the water sat for more than a day or two.

Basement flooding right now?

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