The toilet is arguably the most important fixture in any home. Failure to flush can be a nuisance, but fortunately, it's usually easy to fix.
Toilet Won’t Flush? These Are the Most Likely Reasons and How to Fix It
Updated on Sep. 21, 2024
Many people have experienced the annoyance of a toilet not flushing, and it can turn into a real predicament if you’re in a hurry. Usually, the condition develops slowly enough to give you time to address it with a cool head, but not always. For example, you might be late for work, last in line to use the facilities, and just then, the toilet becomes inoperable. That’s when an annoyance becomes an emergency.
Take heart. According to our experts, Asif Bux and Hendrik Vandepoll, a sudden malfunction is often the easiest to fix. “The simplest things are the most common — a lift chain that has broken or even simply fallen off, or a tank that is not full of water,” says Vandepoll. Long-term sluggish performance culminating in the failure of the toilet to flush at all is a more complicated problem, and while it’s usually solvable, you might not be able to do it if you’re late for work.
Ahead, you’ll find 10 reasons that could explain why your toilet won’t flush and some tips and advice from our experts on what to do about them.
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Clogged Toilet
“A clog in the toilet trap or drainpipe is the most common reason a toilet won’t flush,” says Bux. “This can be due to excessive toilet paper, foreign objects, or waste buildup.” Unfortunately, when this happens, there’s a danger of an overflow if you keep flushing, so the toilet is effectively out of service until the clog goes away.
Fixes to try
- Grab a plunger. Not a flat-bottomed sink plunger, but a bell-shaped toilet plunger. Bux recommends the Korky Beehive Max Plunger, but any brand will do. You should keep one in the bathroom, because plumbers agree it will clear most toilet clogs if you use it properly.
- Pour in some dish soap. The soap may provide enough lubrication to coax the clog out of the way. Plunge after you pour it in.
- Use a snake. “A toilet auger (also known as a closet auger) like the RIDGID K-6 Toilet Auger can help reach and break up deeper clogs,” says Bux.
- Try an enzymatic clog buster. A non-corrosive drain cleaner like Green Gobbler Toilet Bowl Clog Remover may work, but it will take time, so this isn’t an instant solution. Bux cautions to use it sparingly to avoid damaging the plumbing. Whatever you do, stay away from conventional corrosive drain cleaners, which often cause more problems than they solve.
- Pull the toilet and manually clear the clog if nothing else works.
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Misadjusted Float
In a gravity-fed toilet, the float rides on the water’s surface and shuts off the fill valve when the water level reaches the predetermined height. If the float isn’t properly adjusted, it can shut off the valve before the tank has enough water for a flush.
Fixes to try
- Adjust the float arm. If your toilet has a ball float, it’s connected to the fill valve by a rod with a slight bend. Rotate the rod to make the bend face the top of the tank. If the rod is metal and has no bend, go ahead and bend it yourself.
- Shorten the float arm. Turn the rod or the ball clockwise through several rotations to shorten the rod. It must rise higher to develop enough force to shut off the valve.
- Use the adjustment screw. If your toilet has a cup float that rides up and down on the fill valve tube, use a screwdriver to turn the screw on top of the float clockwise. This shortens the rod connected to the fill valve and raises the water level.
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Misadjusted or Disconnected Chain
Vandepoll says that a broken or fallen-off lift chain is a common problem. You can recognize this issue immediately because you won’t feel any resistance when you press the flush valve, and nothing will happen.
Fixes to try
First, you must Turn off the toilet shutoff valve, remove the tank lid and manually lift the flapper or canister to empty the tank’s contents into the bowl.
- Reconnect the chain if it has fallen off.
- Shorten the chain if it’s too long. Disengage it from the hook on the flush lever and reconnect it a few links closer to the flapper. Turn on the water, test the flush and repeat the process if the chain is still too long.
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Leaky Flapper
“On toilets with flappers,” says Vandepoll, “the flapper may be letting water slip past, either due to wear and tear or just an improper fit or adjustment.” Toilets with this problem usually experience “phantom flushing” as the fill valve cycles on repeatedly to replace the water lost through the flapper. You may also see swirling water or bubbles in the tank.
Fixes to try
- Hold the flapper down. For a quick fix, hold the flapper (or canister) down until the tank fills with enough water for a flush. Once you’ve done this, turn off the shutoff valve to avoid wasting water until you have time to replace the flapper.
- Replace the flapper. If the flapper won’t seal, it’s time to replace it. (Most toilets use a standard 2-in. flapper, but some larger ones will use a 3-in. version. If you’re unsure of what size, you can get adjustable Super Flapper, which can be adapted to fit either size.
- Replace the canister seal. If your toilet has a leaking canister instead of a flapper, you simply have to replace the rubber gasket on the bottom of the canister — not the whole canister.
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Malfunctioning Fill Valve
The cylindrical fill valve (most modern ones are plastic) opens to let water into the tank and closes to stop the flow according to instructions from the float. It “may get stuck partway up due to debris in the mechanism, incorrect adjustment or just wear and tear,” maintains Vandepoll, and when that happens, the tank may not fill with enough water for a flush.
Fixes to try
- Jiggle the lever attached to the float. This may dislodge whatever is preventing the valve from opening.
- Flush the valve. Turn off the water, remove the cap (some twist off and some have screws) and turn the water back on again to clear out debris.
- Adjust the valve. Use a screwdriver to turn the adjustment screw on the top of the valve counterclockwise. This should increase the flow.
- Replace the fill valve if you can’t get it to work, or it malfunctions repeatedly. Fill valves are inexpensive (around $15), and the procedure is quick and easy.
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The Refill Tube Has Popped Out
Sometimes, the refill tube, which is connected to the fill valve, isn’t properly aimed toward the center of the overflow tube. If so, all the water from the fill valve goes directly into the bowl and not the tank, so the toilet won’t flush.
Fixes to try
- Reposition the refill tube. It’s made of flexible plastic, so you can bend it until you can get the end inside the refill tube. You can do this without turning off the water.
- Clamp it in place. Some overflow tubes have molded inlets to hold the refill tube in place, while others have special clamps. You’ll usually see the clamp still attached to the overflow tube. If you don’t clamp the refill tube, it’ll probably stay in place for a while, but you may have to fix it again in a few weeks.
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Blocked Rim Jets or Siphon Jet
Rim jets are small holes under the toilet bowl’s rim that release water during a flush. They can get blocked with mineral deposits or debris, reducing flushing power and eventually resulting in impartial flushes.
Fixes to try
- Clean them. Bux’s advice: “Use a small brush or a wire hanger to clean the rim jets.” Mineral deposits are tough to remove, so you’ll need a very stiff brush, or even a wire brush. Don’t worry about scratches; no one is ever going to poke their head in there to see them.
- Dissolve them. “Pour household vinegar into the overflow tube and let it sit for a few hours before flushing,” says Bux. Vinegar is an acid that dissolves mineral deposits, and it’s safe to flush down the toilet, even if you’re on a septic system.
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Sewer Blockage
A few problems are so gnarly that you won’t be able to fix them before going to work, and this is one of them. Fortunately, sewer obstructions take time to develop, so you should have plenty of warning. Flushing will become progressively more sluggish over a period of days or weeks, and the best time to address this problem is before the toilet stops flushing altogether.
Fixes to try
- Try clearing the obstruction yourself. Locate the clean-out nearest the sewer inlet, which may be in the basement or just outside the house. Use a wrench to remove the cap, insert a sewer auger (a long, heavy-duty snake that you can rent) and try to clear the obstruction. You might get lucky.
- Call a plumber. You won’t have any luck if the obstruction is out of reach or if it’s caused by tree roots or something else an augur can’t clear. In this case, you need a plumber with cameras to diagnose the blockage and heavy-duty equipment like water jets to clear it.
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Blocked Vents
According to Vandepoll: “Your plumbing system relies on proper venting to equalize pressure and keep everything running correctly. Vent pipes can get clogged or damaged by things like bird nests, insect nests, leaves, or ice, and this can cause poor water flow or fluctuating water levels in the toilet.”
Vent blockages appear similar to sewer blockages, but Vandepoll points out a key difference: “Normally a vent pipe blockage will cause issues with other fixtures as well, and will not just appear as a toilet problem.” The bathroom sink or shower may drain slowly, and you may hear gurgling sounds from these drains when you flush the toilet.
Fixes to try
- Clear the vent stack. Go on the roof (if it’s safe — otherwise, have a pro do this) and clear the opening of the main vent stack. Shoot a jet of water from a garden hose into the vent opening to clear any obstructions you can’t see. Don’t worry…the water will go into the sewer.
- Melt the ice. It’s common for vent stacks to ice over in the winter, and you must clear the ice. Rather than risking your life walking on an icy roof, go into the attic and use a hair dryer to heat the portion of the stack just below the roofline and melt the ice inside.
- Upgrade the vent. If icing over is a frequent problem, it’s probably because the stack is undersized. A three-inch pipe is recommended in freezing climates, so if yours is only two inches, have a plumber upgrade it.
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Septic System Issues
Homes on septic systems have a special set of potential problems. The inlet to the septic tank may have a screen that can clog, the tank itself may be full, or the whole system may be vulnerable to flooding and backing up when it rains heavily. All of these problems — and more serious ones like a clogged drain field or a malfunctioning transfer pump — can prevent a toilet from flushing.
Fixes to try
- Get the tank pumped. Even if you aren’t having problems, you should do this every three to five years. During this process, the septic pros should be able to identify and fix problems like blocked screens.
- Check the transfer pump. When your drain field is on higher ground than the tank, you need a transfer pump in the tank. If it stops working, check the breaker because it may have tripped (this happened in a house I used to own). Otherwise, have the pump professionally evaluated and replace it if necessary.
- Have a backup plan. If your system is prone to flooding or freezing, you may simply have to stop flushing the toilet until outdoor conditions improve. If so, consider installing a waterless toilet, such as a composting toilet, in an auxiliary bathroom that you can use in emergencies.
About the Experts
Hendrik Vandepoll is the co-owner and service manager of Service Force Plumbing, located in Rockville, MD. He has over 30 years of experience in the plumbing trade.
Asif Bux is the owner and service manager of Comfort Union, a family-owned plumbing, HVAC and electrical service located in Calgary, AB.
