Why Your Sump Pump Runs Constantly

A sump pump that runs constantly is almost always telling you something. The usual culprits are a float switch stuck in the on position, a failed or missing check valve letting pumped water drain back into the pit, a pit too small for the pump so it cycles without pause, or genuinely high groundwater feeding the pit as fast as the pump empties it. Constant running is hard on a pump — it burns out the motor and switch far faster than normal use — so it is worth diagnosing rather than tuning out the hum.

This article focuses on the “runs constantly” symptom. For the full range of sump pump faults, see sump pump not working troubleshooting.

Cause 1: A stuck float switch

The float is what tells the pump when to run — it rises with the water and trips the switch on, then drops and switches it off. If the float gets stuck in the raised position, the pump never gets the signal to stop.

Floats jam in predictable ways. In a cramped pit, the float can catch against the basin wall. It can tangle on the discharge pipe or on the pump’s own power cord. Debris can wedge it. In each case the float is held up, the switch stays closed, and the pump runs on.

How to check it: with the pump unplugged, look at whether the float can travel its full range freely. Gently move it up and down by hand. If it snags on the wall, the pipe, or the cord, freeing it or repositioning the pump so the float has clearance may be all it takes.

Cause 2: A failed or missing check valve

The check valve on the discharge line is a one-way valve that holds pumped water up in the pipe when the pump stops. If it fails — or was never installed — the column of water in the pipe drains straight back into the pit each time the pump shuts off. That refills the pit, trips the float again, and the pump restarts within seconds, re-pumping the same water over and over. The result reads as near-constant running.

How to check it: watch the pit after the pump empties it. If the water level jumps back up on its own with no rain to explain it, and you hear a rush of water falling back down the pipe when the pump stops, the check valve is a prime suspect. The full picture is in sump pump check valves explained.

Cause 3: A pit that is too small

If the pit is undersized for the pump, there simply isn’t enough volume between the pump’s on and off points. The pump empties the small basin almost instantly, shuts off, and the pit refills to the trigger level again in moments. This short-cycling can look like constant running, and it wears the pump the same way.

How to check it: if the pump empties the pit in a second or two and restarts almost immediately even in ordinary conditions, the pit-to-pump match is worth examining. A larger basin, or a pump better matched to the pit, gives the system room to run in longer, less frequent pulls.

Cause 4: Genuinely high groundwater

Sometimes the pump runs constantly because it actually has that much work to do. During heavy rain, a fast snowmelt, or a seasonally high water table, water can pour into the pit as quickly as the pump removes it. The pump runs continuously because the inflow is continuous — a real load, not a mechanical fault.

How to tell it apart: if the constant running lines up with wet weather or a wet season and eases when things dry out, high groundwater is the likely explanation. The pump is doing its job. The real fix here is not inside the pit but outside — grading, gutters, and downspouts that keep water away from the foundation so less of it reaches the pit in the first place.

Matching the symptom to the cause

What you observe	Likely cause	First thing to check (power off)
Pump never stops, pit stays empty	Stuck float in on position	Whether the float moves freely
Pit refills seconds after emptying, no rain	Failed or missing check valve	Backflow down the discharge pipe
Pump empties pit instantly, restarts at once	Pit too small for the pump	Pit size versus pump on/off range
Constant running only in wet weather	High groundwater	Exterior drainage and grading
Runs non-stop in dry weather after checks	Switch or pump fault	Time to call a professional

Why you should not ignore it

A pump running non-stop is operating well beyond the duty it was built for. The motor and the switch — again, the parts most likely to fail — wear out much faster under continuous load, so a constantly running pump is often a pump heading toward failure, frequently at the worst possible moment during a storm. It also uses more electricity and masks the underlying issue. Diagnosing it early is far cheaper than replacing a burned-out pump and cleaning up the flood that follows its failure.

Common mistakes

• Ignoring the hum. Letting the pump run non-stop until the motor burns out instead of diagnosing it.
• Reaching in with power on. Inspecting the float or pit without unplugging the pump first.
• Blaming the pump too soon. Overlooking a stuck float or failed check valve and assuming the pump itself is bad.
• Missing the check valve. Not realizing pumped water is draining straight back into the pit.
• Treating high groundwater as a pump problem. Fighting a wet-season load inside the pit instead of improving drainage outside.
• Improvising repairs. Doing electrical or plumbing work yourself rather than calling a licensed pro.

Work through the float, the check valve, and the pit size with the power off, and note whether the running tracks the weather. Most constantly running pumps trace back to one of these four causes — and the sooner you find which, the more likely you are to fix it before the pump gives out.