Why is my sump pump running constantly? Four causes, in order of likelihood.

A sump pump that runs constantly almost always has one of four problems: a stuck float, a failed check valve, a pump that's undersized for the water coming in, or a water table that's genuinely that high. That list is roughly in order of likelihood, and the first two are things you can check yourself in five minutes. Here's how to tell which one you've got.

We've been fixing sump pumps around Milford since 1979, and April is when this question shows up. The snow's gone, the spring rain isn't, and the clay soil under southeast Michigan is holding every drop of it against your foundation. Some constant running this time of year is normal. Some of it is a pump telling you it's about to die. The trick is knowing the difference.

First, decide if it's actually constant

In a wet April, a healthy pump in a wet yard might cycle every few minutes for days. That's the pump doing its job. What we mean by constant is one of two things: the motor literally never shuts off, or it shuts off and kicks right back on within a minute or two, over and over, even when it hasn't rained. Both of those patterns mean something's wrong, and both of them are killing the motor while you wait.

Cause 1: a stuck float

The most common and the cheapest. The float is the switch, and if it's wedged against the pit wall, tangled in the power cord, or hung up on debris, it can't drop, so the pump never gets the signal to stop. It keeps running in an empty pit, which is the fastest way to cook a motor.

How to tell: look in the pit. If the pump is running and the water is gone, the float is your problem. Unplug the pump, free the float, clear whatever it was catching on, and plug it back in.

Cause 2: a failed check valve

The check valve is a one way gate in the discharge pipe. When it fails, every gallon the pump lifts falls straight back into the pit the moment the pump shuts off. So the pump lifts it again. And again. The pump is running constantly because it's moving the same water in a circle.

How to tell: listen right after the pump shuts off. A healthy valve closes with one solid clunk. A failed one sounds like water rushing back down the pipe, followed by the pump restarting a minute later. The cycle repeats like clockwork whether or not it's raining.

Cause 3: an undersized pump

A pump that's too small for the pit's inflow, or for the height it has to lift the water, never gets ahead. It runs flat out and the water level barely drops. This shows up a lot when a builder grade pump meets a wet lot, or when someone replaced a failed pump with whatever was cheapest on the shelf.

How to tell: watch the pit while the pump runs. If it's pumping continuously and the level is holding steady or falling very slowly during rain, the pump is losing the race. That's a sizing conversation, not a repair.

Cause 4: a genuinely high water table

Sometimes nothing is broken. Parts of Milford, Highland, and White Lake sit near lakes and wetlands where the water table rides high every spring, and in April, after the thaw and a few good storms, the ground is simply full. The drain tile delivers water as fast as the clay can squeeze it out, and the pump runs and runs because there really is that much water.

How to tell: the pump cycles normally (fills, pumps, shuts off, refills), the check valve clunks, the float moves free, and the pattern tracks the weather. If that's your situation, the pump isn't failing, but it is aging fast, and it's the textbook case for a battery backup, because a pump this busy is one outage away from a wet basement.

Why you shouldn't wait this out

Sump pump motors are cooled partly by the water they move. Running dry, or running nonstop for days, overheats the windings and wears the bearings, and a pump that should last 7 to 10 years can burn out in a season or two. Constant running is also how a pump dies at the worst time: it fails during the storm that was making it run. If yours has been at it for a while, check it against the signs a sump pump is failing too.

What's DIY and what's a call

• DIY: freeing a stuck float, clearing debris from the pit, listening for the check valve, watching the cycling pattern.
• Worth a call: replacing a check valve if you're not comfortable cutting the discharge line, anything involving sizing, a pump that can't keep up, or a pit that refills fast in dry weather (that can point to a drainage problem worth diagnosing properly). Our sump pump service page covers what we do.

Quick answers

Is it bad if my sump pump runs constantly?

Yes. Constant running overheats the motor and can burn out a pump that should last 7 to 10 years in a season or two. It's also a symptom of one of the four causes above, so find out which before the motor quits.

How do I know if my check valve has failed?

Listen right after the pump shuts off. A healthy valve closes with one solid clunk. If you hear water rushing back into the pit and the pump restarts within a minute or two, the valve is letting the same water fall back.

When should I call a plumber about it?

Freeing a tangled float or confirming a bad check valve is fine to do yourself. Call when the pump runs with the float clearly down, when it can't keep up with inflow, or when the pit refills fast in dry weather.

Countryside Plumbing is a licensed master plumber serving Milford, Novi, Farmington Hills, and southeast Michigan since 1979. Sump pump repair and replacement is one of our specialties. Free quotes at 248-705-7543.