When a sump pump motor turns on and runs but fails to pump water out of the pit, the issue is typically caused by an air lock trapped in the pump housing, a stuck or broken check valve, a clogged impeller, or a disconnected discharge pipe. Air locks occur frequently when water drains back down too quickly, creating an air pocket that prevents the impeller from priming. Verification: Check the exterior discharge pipe for clogs and verify that the check valve arrow points outward away from the pump.
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