What is a Sump Pump Float Switch and Why Does it Fail?

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If you are a homeowner, chances are you’ve heard of a sump pump, and most likely own one. A sump pump is a small pump installed in the lowest part of a basement or crawlspace. Its job is to help keep the area under the home or building dry and to prevent it from flood­ing. Usually, sump pumps are installed in sump pits. Water flows into the sump pit through drains or by natural water migration through the soil. The sump pump’s job is to pump the water out of the pit and away from the building so the basement or crawlspace stays dry. When sump pumps fail, this can lead to basement floods. The sump pump relies on a float switch in order for the pump to work properly.

What is a Sump Pump Float Switch?

A sump pump float switch detects flooding in the sump; it’s what turns your sump pump on and off in response to the amount of water in the sump pit. The device relies on a round float ball to measure liquid level, like a beach ball that floats on top of the water. When the water rises, the float rises with it. When it gets high enough, a switch inside the float closes and turns on the pump, draining the pit. When the water drops low enough, the switch inside the float opens and turns the pump off. This cycle is repeated hundreds, thousands, and even hundreds of thousands of times during the life of the switch.

What Causes Sump Pump Failure?

The leading mechanical cause of sump pump problems is a switch problem. Here are several common reasons for sump pump float switch failure:


  • Stuck Float Switch – Many times the float simply gets stuck between the pump and the wall of the sump pit, and is unable to rise high enough to be effective. That’s because the pump vibrates slightly whenever it runs, and can “walk” across the bottom of the pit, eventually trapping the float between it and the side of the pit.
  • Overuse/Old Age – Sometimes, after so many up and down cycles, the float switch just gives out and stops responding to the rise and fall of the water in the pit. Often it stops working while the pump is running. When this happens, the pump is left switched on so that it runs continuously until it burns itself out.  
  • Power Failure – Power failure due to bad weather is a recipe for a flooded basement. The float switch and entire sump pump itself run on electricity. A power outage completely immobilizes your sump pump’s ability to drain water.


Arthur Harris provides top of the industry float switches and liquid level control systems to keep your sump pump working properly and your basement dry. Contact Arthur Harris today to learn more and request a quote!