The short answer
Sump pumps most often fail because of power outages, stuck or tangled float switches, pumps that are too small for heavy rain, worn-out motors, and clogged or frozen discharge lines. Many failures happen during the same storms that send the most water into the pit, which is why testing and a backup matter.
The most common reasons sump pumps fail
Power outages
A standard sump pump runs on household power. When a storm knocks the power out, the pump stops at exactly the moment you need it most. A battery or water-powered backup pump covers this gap.
Float switch problems
The float tells the pump when to turn on. If it gets stuck against the side of the pit, tangled in the cord or blocked by debris, the pump won't start even though it works.
The pump can't keep up
During extreme rain, water can enter the pit faster than an undersized pump can remove it.
Age and wear
Motors and switches wear out. A pump that has run for years may fail without warning.
Clogged or frozen discharge line
If the pipe carrying water away is blocked, or frozen in winter where it exits the house, the water has nowhere to go.
Missing or stuck check valve
The check valve stops pumped water flowing back into the pit. If it fails, the pump works harder and can burn out.
Warning signs your sump pump may fail
- the pump runs constantly, even when it isn't raining
- it cycles on and off rapidly
- unusual grinding, rattling or humming noises
- visible rust or corrosion
- water sitting in the pit that the pump doesn't remove
- the pump is many years old and has never been serviced
How to test your sump pump
Slowly pour a bucket of water into the pit. The float should rise, the pump should switch on, and the water should drain quickly. Then check outside that water is coming out of the discharge pipe and draining away from the house. Test before storm season and after long dry spells.
If your sump pump has already failed
Stay clear of water near electrical outlets, check whether the pump has power, and call for help with the water. Sump water is generally treated as gray (Category 2) water, so soaked carpet pad and porous materials may need removal. See sump pump failure water damage for the cleanup process, and our post on sump pump failure and insurance before you file a claim. We can connect you with a provider for water damage cleanup near Chesterfield.