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Garbage Disposal Troubleshooting – The Ultimate Guide

garbage disposal troubleshooting
DIY February 10, 2020
Arthur Brodskiy
Arthur Brodskiy


Garbage disposals are a wonderful modern convenience to have in your kitchen, but like all great gadgets, they can run into problems after repeated uses. Most garbage disposal problems can be fixed without having to call a plumber. In this guide, we’ll go over the “big four” — leaking garbage disposals, disposals that turn on but don’t spin, disposals that won’t turn on at all, and clogs. Finally, we’ll give you a rundown on the things you should never put in your garbage disposal. 


Before we dive in, let’s declare a little golden rule for garbage disposal troubleshooting: keep your hands out of the garbage disposal. Keep this in mind at all times or else you’re going to be googling “garbage disposal injury troubleshooting” next. You can take care of all your garbage disposal issues without putting your limbs at risk. 


Garbage Disposal Is Leaking


Garbage disposal leaks can have a number of causes, so the first step to troubleshooting this problem is to locate the leak. There are four major areas where leaks happen: the sink flange (where the unit connects to the sink), the inlet hose (the line going to the dishwasher), the drain line (the line going to your drain pipe) and the bottom of the unit. 


If you can’t get a clear look at where the leak is coming from, here’s a little hack you can use. Put a plug in your sink and fill it with a few inches of water. Add some food dye or coloring to the water. Now pull the plug and observe under the sink. Take a look at where the colored water is coming from. 


The Sink Flange


One of the more common causes of garbage disposal leaks is the seal around the sink flange getting knocked loose or degrading over time. If the leak is coming from the area right under the sink, and not one of the hoses along the side of the unit, re-sealing the flange will probably solve your problem. It’s a bit of an involved task. You’ll need a flathead screwdriver and plumber’s putty.


1. Turn off power supply to disposal unit


As always, make sure there’s no power going to the unit. That means turning off the switch on the wall and in the circuit box.


2. Unscrew the flange mount, inlet and outlet lines.


Underneath the sink you’ll see your disposal unit. There are two screws underneath the flange where the unit attaches to your kitchen sink. There’s also a set of screws mounting the inlet hose (going to your dishwasher) and outlet line (going to your waste pipes). Remove all the screws. Be careful to keep them in a safe place. 


3. Detach the garbage disposal


Free the unit from the sink by twisting the flange. Keep a hand underneath the disposal unit so it doesn’t get damaged when you release it. 


4. Peel off the old putty and reseal


Once you’ve removed the unit, peel or scrape off any of the old putty around the sink. You have two options to re-seal the area. You can apply new plumber’s putty, or you can purchase a seal that is attached between the sink and flange. 


5. Re-mount the garbage disposal and test


After you’ve resealed the area, you need to put everything back in its place. Re-mount the unit and replace all the screws you removed in step 2. Once everything’s secure, turn the power supply on and and run your faucet while checking under the sink for leaks. 


The Inlet or Drain Lines


Another common location for garbage disposal leaks is around the inlet (to your dishwasher) or drain lines. This is usually caused by a worn out gasket or loose screws where the lines attach to your garbage disposal unit. Simple examine the connection and check the screws. If they seem tight enough, you’ve probably got a worn out gasket, which can be picked up at most hardware or home improvement stores. 


Bottom of the Unit


If you’ve got water coming from the bottom of your garbage disposal unit, you’re most likely looking at a full-on replacement. Often leaks will occur around the “reset” switch or the seal near the power supply. These are all caused by cracks or worn out seals inside the unit itself. The cheaper and more convenient option is to just get a brand-new garbage disposal. 


Garbage Disposal is Humming, But Not Spinning


humming garbage disposal


If you turn on your garbage disposal unit and hear the motor humming but the blades aren’t spinning, the most likely cause is some sort of obstruction in the blades. To troubleshoot this problem, you’re going to attempt to manually get the blades turning to try to knock the obstruction loose. 


1. Turn off power to the unit


Whenever you’re working on your garbage disposal, turn off the power to the unit. This includes the power switch near the unit and the switch on your circuit board. Safety first.


2. Locate the flywheel turning hole


If you look under the sink where your garbage disposal is, you’ll see the unit motor. At the bottom of the unit there’s a hole shaped like an Allen wrench. Garbage disposals usually include their own flywheel tool, but if you can’t find yours you can use an Allen wrench that fits the hole.


3. Manually rotate the flywheel


Using either the garbage disposal tool or an Allen wrench, manually rotate the flywheel. If there’s a substantial obstruction you’ll probably feel some pretty strong resistance. Just keep alternating the direction you turn the wheel in. Keep doing this and you should feel the obstruction break free. Once you get to the point where you can easily rotate the flywheel, you should be good to go. 


4. Other options


If you can’t free the flywheel by using a tool, you might be able to remove the obstruction by going into the garbage disposal through the sink. Now, remember the golden rule. Never put your hand in the garbage disposal. Use a flashlight or your phone to look into the disposal. If you can clearly see something stuck in there, you can try removing it with a pair of long, needle-nose pliers.   


Garbage Disposal Won’t Turn On


garbage disposal not working


If you turn on the garbage disposal and you hear absolutely nothing (no humming or motor sounds), you’re looking at one of the following issues:


  • Your garbage disposal isn’t plugged in.
  • Your garbage disposal needs to be “reset.”
  • The circuit that controls your garbage disposal unit has been shut off. 
  • You have bad wiring on the switch that operates your disposal unit.
  • You need to replace your garbage disposal unit.


We started that list with the most obvious and easy fix, and that’s exactly how you should start troubleshooting the problem. Go down the list and eliminate the possible causes one by one until you either get the unit to work again or start shopping for a new one.


1. Take care of the easy steps


Let’s eliminate some of the easy stuff first. Take a look under your kitchen sink and you should find the outlet that your garbage disposal unit is plugged into. If it’s unplugged, plug it in. If it’s already plugged in and the unit won’t turn on, look for a little “reset” button on the unit. If it’s sticking out, try pushing it back in.


2. Check your circuit breaker/box


If you weren’t able to get your unit up and running again by going under the sink, it’s time to see if the circuit was tripped. Find your circuit box and locate the circuit that controls your garbage disposal unit. Hopefully you have a circuit box that is labeled, but if it isn’t just look for a switch that is in the OFF position. Once you locate the switch, go ahead and turn it on and go back and test your garbage disposal.


3. Check the switch


If resetting the circuit didn’t solve your problem, there’s one last check you can do before replacing your unit altogether. You’re going to have to test the switch that controls your garbage disposal. Before you start unscrewing the switch cover, make sure the circuit lever is turned off. Make sure this stays off the entire time you’re working on the switch.


Next, unscrew the cover plate on the switch with a flathead screwdriver. Once the plate is removed, you should see two phillip’s screws. Loosen those screws enough and you’ll be able to pull the switch free from the outlet. Along the side of the switch you’ll see two wires, each secured by its own screw. 


Examine the wires. If any seem like they’re loose or not fully connected, loosen the screws and move the wires into place. If you suspect you have a faulty switch, you can remove the switch completely and test it with a multimeter, or just replace it. 


When you finish, make sure all screws are fully secured. Go ahead and flip the circuit back to the ON position and test out your garbage disposal unit. 


4. Replace the unit


If you’ve managed to get this far, you’ve made sure the garbage disposal unit is plugged in, reset, there’s power going to the unit and the switch operating the unit is good. That can only mean one more thing: your unit is faulty. Either it has damaged wiring or the motor has burn out. Either way, there’s no sense in trying to repair it. You’re going to need to buy a new unit. 


Garbage Disposal Not Draining


garbage disposal not draining


If your garbage disposal won’t drain, you’ve got a clogged pipe. Some people will assume that the clog is in the unit itself. This is usually not the case. Most of the time, the blockage is in the p-trap (the u-shaped pipe under your sink) or the discharge pipe (the pipe that goes from your disposal unit to your drain pipe). 


Like always, the first step is shutting off all power to the unit. Next, carefully remove the discharge pipe and the p-trap. The trick is to operate very slowly, always having a bucket underneath to catch the water that will inevitably leak out of the pipe fittings. 


Once you have the pieces removed, you should see the obstruction in one or more of the segments. Scrape out all of the solid material and rinse the pieces. 


If you can’t find any sort of obstruction in any of the pipe segments under your sink, you may have a clog somewhere deeper in your plumbing system. In that case, you can use an auger to try to get deeper into the lines, or call in a plumber to deal with the issue. 


Once you’re finished, reattach the p-trap and discharge pipe and test the faucet.


What NOT to Put Down a Garbage Disposal


Garbage disposals are great at taking care of those little scraps of food that are left on your pots, pans and plates. But plenty of homeowners get into the habit of using their garbage disposals and literal trash cans. Putting the wrong things in the disposal will eventually lead to a clog. Not fun. 


Grease, hard materials (bones, shells, pits) and fibrous foods are all things that can cause problems for your garbage disposal. Here are the “big five” things you’re going to want to put in the trash instead. 


1. Cooking grease and oil


Hot grease or oil might seem completely harmless to your garbage disposal blades, and that’s mostly true. The reason pouring oil down your garbage disposal is a bad idea is what grease does to your pipes. When grease and oil cool down, they become solid. Grease buildup on pipes is a common thing that can lead to clogs and even leaks down the road. 


2. Coffee grounds


There are plenty of organic food items that are perfectly fine for your garbage disposal. Unfortunately, coffee grounds aren’t one of them. Coffee grounds have a habit of caking together and forming blockages, especially at the p-trap below your kitchen sink. Put coffee grounds in the trash instead. 


3. Pasta, rice and other grains


Grains are bad for your pipes because they expand in water. If the grains don’t make it all the way out of your drain system, they’ll most likely end up clogging up your p-trap and giving you some serious plumbing headaches. It’s probably unavoidable to put some grains down the drain, but try your best to get most of them into the garbage can. 


4. Bones


Garbage disposal blades are tough, but they can’t handle everything. Bones are way too dense to be chopped up by your disposal blades and are more likely to get caught and jam up your unit’s flywheel. 


5. Eggshells


Eggshells are definitely brittle enough to get ground up by your garbage disposal, but they still pose some problems. Eggshells have little membranes that can get caught up in your disposal unit, which can lead to mechanical problems and even clog pipes further down your plumbing system. 


Wrapping It Up


As you can see, most garbage disposal problems can be easily fixed with some common household tools and a little work. There’s always a few things you can try before you call up your plumber. Then there’s the homeowner’s most powerful tool: preventative maintenance. Being mindful of what you put in your disposal can help you avoid clogs.

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