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Why Does My Sump Pump Smell? Sewer Gas, Dry Traps and Covers
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Check the drain traps first
NDSU Extension says sewer gas can get into a home through basement floor drains and through the drains of rarely used sinks, showers and bathtubs when their water seals dry out. It says the most common sign is a lasting odor near a water fixture, which may smell like an open septic tank, a sewer line or rotten eggs.
- Find the floor drains and rarely used fixtures near the smell.
- Pour in about a quart of water. NDSU says to do this every three to four weeks for drains you seldom use.
- Check again in a day. If the smell is gone, a dry trap was the likely cause.
Check the sump pit cover
- University of Minnesota Extension says the sump must have an airtight, childproof cover. Warm air rising in a house creates negative pressure in the basement that draws moist air in through openings, including open sump pits.
- Ann Arbor's checklist says that if the sump has a clear plexi-glass cover, it must be sealed to the basement floor with new sealant, and concrete screws if needed, to prevent radon from entering the basement through the footing drains and unsealed sump.
These sources do not say whether a covered pit stops a smell. They say a sealed cover limits air and radon coming up through the pit.
Other things the sources mention
- A plugged roof vent. NDSU says moisture can freeze at the sewer vent opening in very cold weather and plug it. A gurgling toilet or poor flushing is an early sign. NDSU says to insulate the vent pipe in the attic. It warns not to use heat tape on attic sewer vents because of fire risk, and to use extreme caution on an icy or snowy roof.
- Health symptoms. NDSU lists headaches, nausea, dizziness and drowsiness as symptoms of sewer gas. Our note: if you feel unwell, get fresh air and talk to a doctor, and call a licensed plumber if the smell lasts after you refill the traps.
Pump not running right too? See sump pump not working. For the discharge side, see where a sump pump should discharge.
Common questions
Why does my sump pump smell like sewage?
We found no extension or government page that explains a sewage smell coming from the sump pit itself. NDSU Extension says sewer gas can enter a basement through dried-out water traps in floor drains and in rarely used sinks, showers and tubs, and that a lasting odor near a fixture is the most common sign. Check those first.
How do I refill a dried-out drain trap?
NDSU Extension says to pour a quart of water into infrequently used drains every three to four weeks.
Should a sump pit have a lid?
Yes. University of Minnesota Extension says the sump must have an airtight, childproof cover, because an open sump can draw moist basement air in through the pit. Ann Arbor says a clear lid should be sealed to the basement floor to prevent radon from entering through the footing drains and unsealed sump.
Can sewer gas make people sick?
NDSU Extension lists headaches, nausea, dizziness and drowsiness as symptoms. It does not mention calling a plumber. If you feel unwell or the smell lasts after you refill the traps, leave the area, ventilate and call a licensed plumber. See a doctor for health symptoms.
Can a frozen vent cause sewer smells?
NDSU Extension says that in very cold weather, moisture in the gas can freeze at the roof vent opening and plug it. A gurgling toilet or poor flushing is an early warning sign. NDSU warns about roof work in ice or snow and says not to use heat tape on attic sewer vents because it can be a fire hazard.
Related guides
Free printable: Sump Pump Fall Check
A ten-minute test before the wet season. Download the one-page PDF now, or get it by email along with a short series of five helpful emails.