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Discussion Starter #1
My sump pump pit was almost full of water and the pump did not extract it as usual. I lifted up the float manually and it did pump and discard a large amount of water about three or four times. Then the water it pumped would flow back, and the pump just expelled it back into the pit. I came back two days later and the same thing happened. I am not very familiar with sumps, so I certainly appreciate any help or ideas. I have only had this pump a few months although I think it was used when I got it.
 

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Yep--Ishmael has it--that is the symptom of a piping system with a bad or missing check valve,,
 

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Discussion Starter #4
No there is no check valve. It is just PVC going up and out to drain. I am just learning about sump pumps and I just read a while ago that there should be a check valve.
 

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Discussion Starter #5
I assume I attach a check valve somewhere up the PVC pipe? I still do not know why the sump pump did not work when the pit was filling up.
 

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I assume I attach a check valve somewhere up the PVC pipe? I still do not know why the sump pump did not work when the pit was filling up.
The pump stands on legs usually about an inch or two long, so if you have an active sump pit (one that sees a lot of water infiltration), then there'll always be a couple of inches of water down there - (with or without the check valve). In other words, the sump will never be completely empty, but, get the check valve on there and the pump will do a more complete job.
 

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You did not post your location, so this comment may be irrelevant. In cold climates, where the drain line is not buried below frost line, you may not want a check valve in your system. The issue with a check valve is that water only flows one way, so if the pipe does not have positive downward pitch, it is likely to remain full of water. In the winter, the water in the pipe can freeze. This is particularly a problem if you get a storm in the Fall, the pipe fills, and there is no flow through the winter. Come Spring, the pipes can be frozen solid. I know this from personal experience (MA).

I removed my check valve about 15 years ago, and I have a small hole (1/8 inch diameter) in the vertical riser just after the pump. This allows any water in the pipe to drain out into the sump pit. Of course, this is irrelevant to you if your pipe is below frost level, or you live in a frost free environment.
 

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Maybe the output pipe is partially clogged now. Maybe the float switches are stiff or jammed so the pump does not come on by itself when needed.

If there is a bleed hole in the pipe (sometimes needed as described above to prevent filling and freezing of the output pipe) then the pump will always spray some water back into the pit when running. The pump works okay because the amount of water going back into the pit and having to be repumped is (should be) a very small fraction of the water being expelled to the outside so the pit still empties quite quickly.

How does the behavior of the pump now differ from the behavior of the pump before you thought that something was wrong? (essay question)
 

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Discussion Starter #9
How does the behavior of the pump now differ from the behavior of the pump before you thought that something was wrong? (essay question)

Usually the pump engages long before the waer gets that high. I guess I could test it by spilling water into the pit and seeing at what point the pump does purge the water.
 
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