A sump pump is a first-line defense against flooding, but even a device as important as a sump pump can have bad days too. A sump pump that is running but not pumping could be caused by more than one factor. In this article, we’ll discuss the possible reasons why your sump pump is running but not pumping.
Sump Pump Running But Not Pumping
Before any repairs, you’ll need to confirm if your pump actually has a problem. You can do that by filling the sump’s basin with water-high enough that the water level raises the float, activating the motor. Once this happens, check the end of the discharge pipe to see if water is coming out.
If you only hear the motor pumping, but the water level in the basin isn’t dropping, your sump pump isn’t working properly. To make things easier, try sticking a ruler vertically into the pit so that you know exactly how much water is in the pit and if any amount of water, no matter how small, has left the pit.
Reasons Why your Pump isn’t Draining Water
Clogged Drain Lines
This is a common cause of a sump pump not pumping out water. When the pumped water can’t exit the end of the discharge line, it will remain in the pit. This doesn’t mean the pump will automatically go off.
This is because as long as the float senses water in the sump’s basin, the pump’s motor will keep running. A clogged drain line can be caused by many factors, including debris, sediments, and other materials that fall into the sump basin.
If you have a sump pump clogged with sediment, you don’t necessarily have to replace the entire pump.
Instead, there are ways to unclog the said pump. You can prevent clogged pumps by not leaving the sump pump open, keeping leaves out of the lines, and conducting the normal scheduled maintenance on the pump.
How to Unclog a Sump Pump?
First, go outside and examine the discharge line. The pump could get clogged by dirt, leaves, and other sediments depending on the position of the pump outdoors. If the discharge line is clogged, you can use a coat hanger to help loosen and unclog the sump pump. If, after doing this, the pump is still not pumping water, then the inside of the pump may be clogged. 
First, unplug the sump pump. Then, shut off the breaker to make poking around in the pump safer. Next, inspect the inlet screen of the pump-the small opening where water enters the pump.
You can use a flashlight for a better view, and if you still cant see well, disconnect the discharge line and lift the pump out from the pit.
Remove any dirt that may be clogging the inlet. Remove as much sludge as possible and use a rag to clean up the rest. Use this opportunity also to clean up any debris or dirt stuck to other parts of the pump to prevent future clogging.
Now place the pump back into the sump pit and reconnect the discharge pipe. Next, plug the pump back in and test run it by pouring a bucketful of water into the pit, high enough to raise the float switch.
If the pump begins to pump out water, you’ve successfully fixed the problem; if not, there is another lingering problem yet to be identified.
2. A Broken Impeller
A sump pump’s impeller is partly responsible for generating the force required to push collected water down the drain lines. It is often located inside the pump behind a screen that is designed to prevent sediments from clogging or damaging the impeller.
Unfortunately, this part is quite sensitive and can easily get damaged by small stones and other debris. Over time, sludge and debris can also clog the impeller, making it not spin properly.
If the impeller gets broken or dented so that it can’t spin properly, you may have to replace the impeller. You can tell if your impeller is not working by placing your hand on the body of the pump while it is running. Then if it’s working, you should be able to feel it spinning. 
Protect your impeller by preventing debris and sediments from entering and damaging it.
How to Check and Replace a Pump’s Impeller
Once again, unplug the sump pump and disconnect it from the discharge line. Depending on the type and make of the sump pump, you might have to remove the bottom casing to access the impeller.
If you’re confused about the position of your sump’s impeller, consult the manufacturer’s manual for confirmation.
Once you’ve taken the impeller out, visually inspect it for any noticeable damage. If it is damaged, you’ll have to replace it. If the impeller has simply fallen off, a thread will usually be attached to the impeller or to the rest of the motor.
To put the old impeller back on(or to install a new one), thread the impeller back on but not completely. Next, give the impeller a quick spin so that it fits into place.
Don’t worry about further tightening. The threads are reversed threaded in such a way that when the sump is running, it will do the remaining tightening itself.
Replace the bottom cover and place the sump pump back into the pit. Ensure the pump is level. Reconnect the discharge lines and plug the pump back in. Turn the breaker on and test-run the pump, as mentioned before.
Hopefully, the pump will start to pump out water now. But, if that’s not the case, all hope is not yet lost.
3. Burned out Motors
Overworked and low-quality pumps most commonly cause this. If the sump pump’s motor is too small, water may enter the sump basin faster than the pump can pump it out.
This will cause the motor to run continuously, eventually leading to burnout. A motor could also burn out naturally over time. In all these cases, the motor will have to be replaced.
It is advisable to install a pump that corresponds with your needs. Manufacturers also recommend that your pump be plugged directly into an outlet and that the outlet be the only thing powered by the circuit breaker/fuse that feeds it.
4. A Broken Check Valve
A check valve is a one-way valve that only allows water to move in one direction and, in this case-out of the sump basin into the discharge lines. This valve prevents water being pumped out of the pit from flowing back into the sump pit.
If the check valve is broken, the water being pumped out of the pit will flow back in, decreasing the amount of water removed per cycle while also increasing the frequency of cycles, which will cause the pump to run continuously and inadvertently lead to the pump failing prematurely. You will also have to replace the check valve if it’s broken.
If you’ve checked all these and the sump pump still isn’t responding, then you should consult with a professional technician or consider replacing the sump pump entirely. 
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Listed above are some ways to resolve a sump pump that runs but doesn’t pump out water. If all these fail or you don’t have enough time on your hands to go through all the processes, your next best option is to consult a technician. If the sump pump still can’t be fixed, the technician can recommend and install a replacement.
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Michael Davis is a heating & plumbing expert who currently works as independent contractor in SC. He also writes for Plumbertip.
For almost 10 years he worked on various plumbing tasks across South Carolina.