A residential building's foundation drain discharges to a sump pit located inside the basement. The sump pump motor runs continuously but fails to lower the water level effectively, and signs of water infiltration are visible at the basement floor/wall joint. What is the most likely cause?

Question: A residential building's foundation drain discharges to a sump pit located inside the basement. The sump pump motor runs continuously but fails to lower the water level effectively, and signs of water infiltration are visible at the basement floor/wall joint. What is the most likely cause?

Answer options:

• The sump pump's 'on' float switch is set too high. ✅ The check valve on the sump pump discharge line is faulty or missing.
• The foundation drain tiles are completely blocked with silt.
• The municipal storm sewer is surcharged, causing backflow into the sump.

Correct answer: The check valve on the sump pump discharge line is faulty or missing.

Explanation: If the sump pump runs continuously and water level does not drop, a faulty or missing check valve allows pumped water to flow back into the sump pit once the pump shuts off, or even while it's running, leading to an endless cycle. While blocked drains or a surcharged municipal sewer could cause high water, the continuous running of the pump without level reduction points directly to the check valve failing.