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Sump pump backflowing?

2038 Views 5 Replies 3 Participants Last post by  Richo
Just tonight I heard the alarm from my battery back up sump pump go off.

Went downstairs and the main pump was running non stop and not pumping anything. I unplugged the pump, and then plugged it back in and then it pumped out the pit so I thought it was OK.

An hour later I heard the alarm again so I went down and the same thing happened. Unplugged the main pump, waited and plugged it back in and it worked again. However when it stopped I noticed what seemed to be water backflowing into the pit.

At this point I lifted the float and it started running but it was just agitating the water in the pit and not pumping, even though I could hear some water moving in the discharge.

I disconnected the main check valve to see if it's holding water back and it is, as I got sprayed in the face when I loosened the hose clamp :laughing:

Here is a diagram of how it is configured. The red arrows point to check valves. The upper one is not necessary but I still use it as a safeguard.

So anyways, I'm not sure where to go from here to diagnose the problem. Any help would be appreciated.
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#1 Go back and add your location to your profile.
Yes it's important, depending on where you live and how it was run the outside line could be frozen.
#2 There's no cheak valve between the primary and secondary pumps.
Source of least restance would have the second pump just pumping water back into the sump.
I also would have them in two differant lines.
Profile updated. I'm in WI and yes, it's cold here, but if the discharge line were frozen, the backup pump would fail as well, and that one is working. Plus the primary pump did work a couple times when I was testing it, and it pumped out plenty of water at its normal rate.

There is a check valve between the 2 pumps (red arrow at the bottom of diagram) which prevents the backup pump from discharging into the primary pump.

I know that a separate discharge is recommended but this pump was designed to work on the same discharge, which is the reason I bought it.

To sum it up, the primary pump is working sometimes, other times just cycling, and the primary pump is working every time.

I am trying to analyze where the primary pump could be going wrong. All I can come up with is that maybe the check valve on the backup pump (center red arrow in drawing) is failing causing the discharge to cycle back into the pit through the secondary pump.

Does this seem like the first logical place to look?
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Follow up

When I installed the backup pump this past summer the sump pit was clear. Now there is some dirt in the bottom of it and several pieces of gravel. It is a plastic sump pit so the dirt and gravel had to have come in through the drain tile.

Could it be that the pump sucked up a small piece of gravel that became lodged in the check valve? And if this is a possibility, how should I try to prevent this from happening?

I disassembled the discharge and cleaned the check valves and they did not appear to be obstructed at all, but the pump ran fine this morning when I plugged it in.
A screen over the intake of the sump pump should keep out debris that can hold the check valve ajar.

But the intake must be designed to have such a screen, including being of a larger diameter than the outlet pipe.

This does not guarantee perfect reseating of the check valve after each cycle and you may still need to take it apart and clean the check valve every so often.

With two pumps using the same outlet, a check valve is needed at each pump. In that configuration a third check valve, higher up, is not needed except as an extra layer of defense against imperfect reseating, or if there is a bleed hole in the outlet pipe just below the pit cover level to prevent air lock or water hammer.
I did see a suggestion to place the pump on top of a brick paver to help reduce the chance of it sucking up debris off the bottom of the pit.

I don't know how much that helps but it is worth a try.

Thanks for the reply.
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