A sump pump that runs constantly is either dealing with more water than it can handle, or something mechanical has failed. It’s rarely normal, and ignoring it usually leads to a burned-out motor, a flooded basement, or both.
Here’s what’s most likely causing it, roughly in order of how often I see each one.
Stuck or Misaligned Float Switch
This is the most common culprit. The float switch is the trigger that tells your pump when water is high enough to run. If it’s tangled in the pit, resting against the side wall, or jammed in the “on” position, the pump never gets the signal to stop.
Before calling anyone, unplug the pump and look in the pit with a flashlight. If the float is wedged against the wall or tangled, try freeing it. If the pump keeps running after that, the switch itself has likely worn out. That’s a plumber call: getting it set at the right water level matters, and it involves the wiring.
High Water Table or Drainage Issue
If the float is working fine but water just keeps coming, the pump isn’t broken. It’s overwhelmed. This happens when groundwater is naturally high around your foundation, when you’ve had heavy rain, or when drainage around the house is directing water toward the pit instead of away from it.
A pump running constantly during or right after heavy rain is less alarming than one running continuously on a dry day. Dry-weather cycling that won’t stop often points to an underground water source, a cracked foundation letting in groundwater, or a neighboring property’s drainage pushing water toward yours.
Failed Check Valve
The check valve is a one-way valve on the discharge pipe. Its job is to keep water from flowing back into the pit after the pump shuts off. When it fails, water drains back in as soon as the pump stops, the float rises again, and the cycle restarts immediately.
You can sometimes hear this: the pump runs, stops, then kicks back on within seconds. That rapid short-cycling is a clear sign the water is coming back in from the discharge line rather than rising from below. A plumber can replace the check valve, and it’s usually a straightforward repair if caught early.
Undersized Pump for Your Pit
If your home has a lot of groundwater, or the original pump was chosen for a low-water situation that’s since changed, the pump may simply not have enough capacity to outpace the inflow. It runs because it can’t get ahead of the water.
Sump pumps are rated by horsepower and gallons per hour. A basic 1/3 HP pump handles modest conditions. Homes with persistent water issues often need 1/2 HP or more. Some homes also benefit from a backup pump alongside the primary, though the main reason to have a backup is power-outage protection: if both pumps run on electricity and the power goes out during a storm, neither will run. Getting the sizing right requires knowing your pit’s inflow rate, which varies seasonally.
How a Plumber Diagnoses This
A licensed plumber will start by watching the pit. How fast does water rise? How quickly does the pump clear it? Does water come back in immediately after the pump shuts off? That last detail points straight to the check valve.
They’ll also check the float switch by hand, inspect the discharge line for blockages or improper slope, and look at where the discharge terminates. If it’s discharging too close to the foundation, some of that water finds its way back in. They’ll also assess whether the pump’s horsepower is matched to your actual conditions.
If groundwater is the issue, they may suggest a perimeter drain or other mitigation depending on what’s driving the water table.
What to Check Before Calling
A few quick observations can help you describe the problem accurately and let the plumber diagnose faster:
- Look at the float in the pit (unplug first). Is it wedged against the wall or tangled? If freeing it stops the cycling, problem solved. If not, you’ve confirmed the switch is the issue.
- Pour a bucket of water into the pit and watch what happens after the pump shuts off. If water immediately rises again, the check valve is failing.
- Check the discharge line outside. Is it blocked by debris or ice? Does it terminate at least 10 feet from the foundation?
- Look at the pit walls. If water is seeping through cracks, note that. It changes the diagnosis.
Anything beyond that, including replacing the check valve, sizing a new pump, or figuring out why water is entering during dry weather, is work for a licensed plumber.
When to Call a Licensed Plumber
Call sooner rather than later if:
- The pump is running in dry weather with no obvious explanation
- The pump cycles on and off rapidly, stopping and restarting within seconds to minutes
- The pit has standing water despite the pump running
- The pump is making new noises: grinding, rattling, or a strained hum
- Your pump is more than 7 to 10 years old and showing any of these signs
A pump that’s been running constantly for days is heading toward burnout. A dead pump during a storm is a flooded basement. Get it diagnosed before storm season, not after.
This site is an information-only guide, no plumbing services offered. When you’re ready to have someone out, hire a licensed plumber and verify their license at cslb.ca.gov before the work starts. Takes about 30 seconds and confirms they’re insured and in good standing.