A float switch determines when the sump pumps turns off and on. As water rises in the pit of the sump pump, this switch floats up, and when the water reaches a certain level the sump pump is automatically turned on. When the sump pump is jammed or backed up, the switch may stick in the "on" position. Sump pump vibrations may also leave the float switch in the "on" position. A jammed sump pump requires servicing, so call your local sump pump technician.
A constantly running sump pump may indicate that the device is too small for its use. While a smaller pump may be cheaper, if asked to handle more than its capabilities on a regular basis, it is likely to break down. Make sure you are not overfacing the pump, and check its specifications before installation to avoid early replacement. If the sump pump runs continuously due to inadequate size, the only way to address the issue is purchasing and installing a properly sized model.
The sump pump's liner may be the culprit. Even if the sump pump size is adequate for the service area, its liner may not be. This results in the sump pump sending water out of the building more quickly than the liner fills. The sump pump then keeps running or constantly switching on and off, referred to as short-cycling. To maintain the integrity of the sump pump, install the right-sized liner.
Sometimes a sump pump runs continuously due to an electrical problem you can troubleshoot yourself. If the pump cord and the cord of the float switch are plugged into separate outlets, try plugging the pump cord into the additional connector on the rear or side of the plug on the float switch. Put the combined plugs into one outlet receptacle to see if the sump pump starts running normally. If this does the trick, make sure to have the non-working outlet repaired.