I have a sump in my basement that collects water from (I believe) outside of the house through some kind of foundation drain / weeping tile.

Lately with all of the snow melting and rain, I've noticed that the electric sump pump is not always kicking in on its own. Sometimes it does, but often I hear the backup (water-based) pump instead.

I've taken a look down the sump and it looks like the float for the switch is rising but still isn't engaging the pump. If I gently jiggle the discharge pipe, it kicks right on.

See this video, with the electric sump pump in the bottom-center of the frame (green) and the white float right above it (note the water level is already at/above the float): https://vid.me/IM6i

The float seems to rise but at some point, the water level rises over it. Could the float be waterlogged, so it does not have enough buoyancy to engage the pump? Or could it be something with the rod that connects the float to the pump? Why does it happen intermittently?

How should I go about investigating further?

Thanks for the help.

  • Joseph: ANy chance you could share how you finally resolved this issue? I have a Zoeller M53 that has the exact same issue...water rises above float and just the slightest touch triggers the switch. Replaced the switch and still having same problem. Replaced the float and guess what...same problem. This is about as frustrating as it gets. I have checked over and over and it is not binding. just not enough upward pressure to push the switch on...yet it has worked for years with no issue.
    – j crow
    Sep 8, 2018 at 17:32

2 Answers 2


The float should travel freely up and down on a vertical rod.

As the float rises toward the top of its travel, it operates a switch. This is the switch that turns on the pump.

Raise the float manually. The switch should operate and the pump should turn on. If it does not, it is the power supply, the switch or the pump.

It should be obvious just by looking at the float whether it is floating or not.

  • The float does move up and down . You can see it moving back down in the video I posted as the water is discharged. The trouble is that, even though the float does rise, sometimes the water continues to rise above the float. I do not know if this is because the float is not buoyant enough or if there is resistance for some reason with the rod/switch.
    – Joseph
    Apr 1, 2017 at 15:39
  • 1
    @Joseph It's not enough for the float to move up and down. It must also interact with a switch at some point. If you move it up manually, you should be able to hear/feel the switch operate, unless it is magnetically actuated. When the switch operates (if), the motor should fire, so watch out. You're looking to see what seems reliable and what seems not. More likely than not, it will be apparent. For instance note the switch operating force and feel if the float likely has enough bouyancy to operate it. Apr 1, 2017 at 15:58

A waterlogged float will be audible if you remove it from the pump and shake it.

IMPE the rod/top mount motor arrangement is often subject to flaky operation as some part of the mechanism binds, sometimes, not always, just enough to prevent it from turning on.

I have found fully submersible sump pumps far more reliable, but my workplace still chooses the cheapest pumps with the top motor, which can be expensive when you count the cost of the occasional flood. But that's why I'm familiar with their issues. The fact that "jiggling" causes it to work suggests (to me) binding in the float mechanism or a defective switch, and binding is far more common.

If the pump is not vertical or the rod-support is not lined up with the switch properly, the odds of binding increase. Check the float/rod system for free and easy movement (manually) and adjust as needed. Test with a hose or a bucket of water, adding water to the sump to check turn-on. Or take the more expensive road and get a submersible sump pump to replace it.

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