Toilet Overflowing or Overfilling? Here’s What To Do

If you have ever clogged a toilet, you already know the panic that sets in as the water in the bowl rises and continues to rise past its normal level. Like most people, you probably stare at it, willing it to stop filling. When you finally realize it isn’t going to stop on its own, it is usually already too late. The water spills over the top of the bowl and begins flooding the floor. 

As stressful a situation as this is, it is an all-too-common occurrence in many households. Toilets are one of the most-used appliances in the home, which means they can be prone to malfunction from time to time. It is easy to take the toilet for granted, and when it stops working, it can be a devastating feeling. 

If you are dealing with a toilet that overflows or a toilet tank that overfills, you need to get to the root of the issue, so it doesn’t continue to happen. There is little more infuriating than having to clean up dirty toilet water – or worse – replace the floor and walls because your toilet overflowed and caused severe water damage. 

In the paragraphs that follow, I’m going to give you several reasons why your toilet may be overflowing or overfilling and what you should do if it happens. Don’t worry… Most of the fixes for these issues you can do yourself, but as always, you can enlist the help of a plumber if you aren’t comfortable with or can’t make the repairs yourself. 

Why Your Toilet Bowl is Overflowing

The most common reason toilets overflow is a blockage somewhere along a home’s sewer system. In most cases, the clog occurs within the toilet itself or just beyond it in the drainpipe. In some instances, the clog may occur in the vent pipe that regulates airflow in a home’s sewer system. Whatever the case, you must determine where the blockage is and remove it to get things flowing freely again. 

Clogged Toilet

If your toilet itself or the drainpipe leading away from your toilet is clogged, water will rise in the bowl of the toilet and continue to do so, spilling over the rim of the bowl. You will know that the problem is in the drain because the water will only overflow from the bowl and not the tank. In most cases, clearing a blockage of this nature is as easy as plunging the toilet. 

Blocked Vent Pipe

Once in a while, a blockage occurs in the vent pipe that regulates airflow in your home’s sewer system. Most people don’t know that a sewer vent pipe even exists and that it is located (usually) on the roof. 

When you flush the toilet, the vent pipe allows the noxious gasses in your home’s sewer system to escape, thus keeping these gasses from entering your home. If a blockage occurs in this pipe, however, air cannot flow freely through the system, and your toilet may overflow. If the problem occurs in the vent pipe, a trained plumber will need to come out and clear the blockage for you as it requires specialized equipment and climbing on the roof. 

Why Your Toilet Tank is Overfilling

While an overflowing toilet bowl is rather simple to diagnose and fix, an overfilling toilet tank is a little more complex. There are a few things that could be causing it, with the most difficult part is figuring out which is the culprit. Once you have figured out what the problem is, fixing the issue is relatively easy.

A Misaligned Overflow Tube

The overflow tube inside your toilet’s tank is responsible for making sure any excess water is diverted into the bowl so that the tank doesn’t overflow. This tube must be aligned just right to prevent overfilling. 

Each time you flush your toilet, the rubber flapper at the bottom of the tank opens to allow water to flow quickly into the bowl. This fast-moving water is what carries the waste down the drain. Afterward, the tank fills back up and is ready for the next flush. 

If you take the cover off your toilet tank, you will find a white tube in the middle. This is the overflow tube. As the tank refills after flushing, the overflow tube’s job is to divert excess water into the bowl should the water level rise too high

What regulates the water level?

The overflow tube does. If the tube is out of alignment (or set too high), water may overfill the tank and cause flooding. 

A Leaky Fill Valve

While a misaligned overflow tube is easy to spot, a leaky fill valve is a little more difficult. You may not physically see the issue, but you will likely hear it if your toilet’s fill valve is to blame. 

What do I mean by this? 

If your toilet continues to ‘run’ after the flush cycle has finished, there is a good chance that the fill valve is bad. The fill valve is located at the bottom of the toilet tank. It is where the water supply hose is connected to the toilet. Over time, this part can wear out, which can cause it to constantly leak water into the tank even when the toilet hasn’t been flushed. If the overflow tube is working as it should, the excess water will drain into the bowl and the water will continue to fill the tank. A telltale sign that your toilet’s fill valve is faulty is hearing your toilet ‘running’ when not in use. 

High Filler Float

Newer toilets have a fill valve float, while older models have a ball float. Whichever one your toilet has; their jobs are the same: to regulate the water level in the tank during the filling process. If the fill valve float or ball float is set too high, the water will continue to fill beyond its recommended level. The excess water will then exit via the overflow tube. The result is a perpetual cycle of filling and draining that wastes water and causes undue wear and tear on your toilet’s inner workings. 

What To Do When Your Toilet is Overflowing

When your toilet overflows, the first thing you need to do is not panic. Take a deep breath and follow the steps below to stop the fill of water and diagnose the issue. 

1. DO NOT flush The Toilet!

If the water in the bowl is rising past its normal level, it means there is a blockage somewhere that isn’t allowing water to pass by. If you flush the toilet again, you will be adding even more water that won’t be able to pass the blockage, thus increasing the odds of flooding your bathroom. 

2. Open Toilet Water Tank and Push the Flapper Shut

Take the lid off the tank and locate the flapper. The flapper is a rubber circle at the bottom of the tank. It is attached to a chain and is likely in the open position, allowing water to flow into the bowl. Push the flapper shut to stop the water from entering the bowl. 

3. Turn off the Water Flow at the Inlet Valve

The water inlet valve is usually found underneath the toilet tank where the water supply hose is attached. Turn the valve clockwise as far as it will go to turn off the water and prevent any more water from entering the tank. 

4. Check the Water Float is In Position

Now that the water won’t flow into the tank anymore, check the float mechanism. If your toilet is newer, it may have a float cup. If it is an older model, it will have a float ball. Check that the float valve is in the correct position. 

If you have determined that the overflow issue is caused by a clog somewhere in the system, rig the float to stay in the position it is in to prevent more water from entering the tank until you have cleared the blockage. 

5. Check the Overflow Tube is Aligned

If your toilet is experiencing overfill issues due to a misaligned overflow tube, you will need to adjust the tube so that it can deal with excess water properly. For an overflow tube that is too long, you can use a hacksaw to remove the excess length. 

You can certainly DIY this task but don’t feel bad if doing so intimidates you. Feel free to call a plumber to shorten the overflow tube if you are worried about doing it incorrectly or damaging other parts of your toilet. 

6. Check the Trap and Waste System for Clogs

Finally, to remove a clog in the trap or beyond, don some rubber gloves and grab a flange plunger and a bucket. If the

is so high that it will spill out when you start plunging, use the bucket to remove some of the water. Make sure to create a tight seal with the plunger and use a firm up-and-down motion for 10-20 seconds to dislodge the blockage. If you clear the clog successfully, the water in the bowl will drain out. 

Once the blockage is cleared, untie the float, and turn the water supply back on. The tank should start filling. Once it is full, flush the toilet to make sure everything is flowing freely once again. 

Plumber and HVAC Technician | Website | + posts

As a retired Master Plumber Jamie has over 30 years of hands-on experience, making his plumbing knowledge second to none. He has also worked on both residential and commercial HVAC installation and repair projects.