Basement flooded over the weekend. The same type of flooding has occurred 3 times in the last 6 years. The sump pump was replaced during the first occurrence. However the problem continues to occur. I tested the sump pump it does work. The only thing I can think of is that the sump pump motor is underpowered and can’t keep up with large amounts of water / rainfall. It’s hard to tell from the label but it looks like the sump pump has a 1/3 HP motor. See photos.

Looking for some advice on how to address this problem. Do I upgrade the pump to something with a bigger motor? Battery back pump? Other ideas?

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UPDATE The problem is at my moms house. After further investigation, it appears the problem is with the discharge pipe. It’s dumping the water back into the system. See photo. I need to extend this discharge away from the house. Any tips on to do this? I know ultimately I need to dig a trench and slope it away from the house, but short term can I just hook up a flexible tube to it so it drains away about 8ft?

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  • Would need to know the max gals/per hour coming in to size a size sump pump right. Might just be easier to have two or three regular pumps at different levels to handle the excess.
    – crip659
    Commented Aug 26, 2023 at 22:42
  • Is the pump losing power? What is the GPM rating, how many gallons per minute can the pump handle?
    – matt.
    Commented Aug 26, 2023 at 22:45
  • Can you show a wider picture, which might inform possible improvements other than "get a bigger pump?"
    – Ecnerwal
    Commented Aug 26, 2023 at 23:55
  • 1
    Sanity check: Have you tested that pump, and it's exhaust pipes,by running water through it? That could also be a way to measure how many GPM it's actually able to move to the necessary height. (My small pump moves about 8 GPM up 8' despite resistance in the flex hose attached outside. That was sufficient for my 100-year flood. Of course with climate change that probability has undoubtedly shifted...)
    – keshlam
    Commented Aug 27, 2023 at 0:19
  • Not enough information to know if the pump is underpowered or not. Were you able to observe the pump at the time the basement was flooded? If so, was the pump continually running and just not able to keep up with the water in your sump pit, or was the water coming in elsewhere? Also need to know what sort of piping (distance, height the water needs to be raised to exit, etc.) to help identify if there could be restrictions in the output that is limiting the outflow. Also, was this a time of unusually heavy rain that would cause the pump to be overwhelmed?
    – Milwrdfan
    Commented Aug 27, 2023 at 3:19

1 Answer 1


Multiple possibilities.

You could go with a bigger pump. You could go with a second pump, and (ideally, but it's costly, but the cost comes with better reliability) a float switch setup that powers each pump alternately for low water (so one pump isn't sitting there doing nothing all the time until it doesn't work) and both pumps when water gets higher. If you have problems with the power going out during rain events there are battery and (if municipal water is available) water-powered backup sump pumps.

Might be the power of the pump, might be internal wear of the pump parts, might restrictive plumbing limiting the output (I can't begin to guess how many times I've see a sump pump with a 1.5 or 2 inch output choked down to 1" pipe "because it's cheaper".)

As far as I can infer (letters before numbers don't quite match current products, and the numbers are not quite clear) that appears to be a 1/3 HP Zoeller pump with a 1.5" discharge pipe connection, rated for 43 gallons per minute at 5 feet of head. If it has to pump up a lot higher, flow will be reduced, possibly drastically. If the pipe is not 1.5 inches, flow will be reduced. If you get 80 gallons per minute in when the basement is flooding, you need more pump capacity.

Due to design of the pump itself, you can get cases where a 1/3 HP pump would be fine, but one optimized for more head (height it lifts water, and pipe-friction backpressure) may be needed, since a pump designed for a lot of flow at low head is impacted heavily by additional head, and a pump designed for additional head may pump a lot more water at greater head with its different design, on the same power, even though it would pump less at lower head. So don't just look at pump horsepower, especially if your water needs to go up 10+ feet or has a very long pipe.

I've also seen cheap sump pumps where the float will stick and not turn the pump on, sometimes, but not always. I think that's less likely for the type you show.

Depending on terrain, you may or may not be able to greatly reduce the load on the sump pump by providing a gravity drain to daylight. That requires somewhere downhill you can run a pipe to, so it doesn't work if you're in a flat area.

Depending where the water comes from, you may be able to reduce the load (even in a flat area) by altering the grade around the house so water on the surface runs away from the house, not towards it or nowhere. Only takes about 1/8" per foot.

If you don't have gutters, or you do but the downspouts are not routed away from the house before dumping, or they need repair/cleaning, that can help. For that matter, if the sump discharge is too near the house you can end up pumping the same water in circles.

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