How to Fix a Running Toilet: The 4 Causes and How to Fix Each One

That hissing sound from the bathroom is not normal, and it is not harmless. A toilet that runs constantly wastes up to 200 gallons of water a day. On a metered water bill, that can add $50 to $100 a month. The worst part is that the fix is usually a $5 to $10 part and about 15 minutes of your time. If you want to know how to fix a running toilet, start here. I will walk you through the four causes and the exact fix for each.

Why Your Toilet Runs Nonstop

To understand how to fix a running toilet, you need to know how it works. The tank holds water. When you flush, a rubber flapper lifts and lets water rush into the bowl. Then a fill valve refills the tank until the water reaches the right level, and a float shuts the valve off. A running toilet means one of those parts is not doing its job. The water is either leaking out of the tank into the bowl, or the fill valve never shuts off. That is it. Every running toilet is one of those two problems, caused by one of four parts.

Cause 1: The Flapper Is Worn Out (Most Common)

This is the culprit about 80 percent of the time. The flapper is the rubber seal at the bottom of the tank. Chlorine and minerals in the water eat away at the rubber over a few years until it stops sealing. Water leaks slowly into the bowl, the tank level drops, and the fill valve keeps topping it off. That is the running sound.

How to check: Put a few drops of food coloring in the tank and wait 15 minutes without flushing. If the bowl water turns colored, the flapper is leaking.

How to fix: Turn off the water valve behind the toilet and flush to drain the tank. Unhook the old flapper from the pegs on the overflow tube. Take it to the hardware store to match the size. A Korky universal flapper runs about $5 to $8 and lasts longer than the cheap ones. Snap the new flapper on, reconnect the chain to the flush lever with about half an inch of slack, turn the water back on, and test. Total time: 15 minutes.

Cause 2: The Fill Valve Will Not Shut Off

If the water level in the tank is too high, water pours into the overflow tube nonstop and the valve never closes. You will see water visibly running into the overflow tube, which is the tall hollow pipe in the middle of the tank.

How to check: Lift the tank lid. If the water is at or above the top of the overflow tube, the fill valve is set too high or is broken.

How to fix: Most fill valves adjust with a screw or a squeeze clip on the side of the valve. Turn the water on, let the tank fill, and set the level to about one inch below the top of the overflow tube. If adjusting does not work and the valve keeps running no matter what, the valve is worn out. A Fluidmaster 400A universal fill valve costs about $10. Shut off the water, unscrew the water line under the tank, unscrew the old valve, drop in the new one, and reconnect. Fifteen minutes, basic hand tools only.

Cause 3: The Chain Is Tangled or the Wrong Length

The chain connects the flush lever to the flapper. If it is too short, it holds the flapper slightly open and water leaks through. If it is too long, it can slip under the flapper and keep it from sealing. Either way, you get a running toilet.

How to fix: With the flapper closed, the chain should have about half an inch of slack. Not tight, not dragging. Move the chain hook up or down a link on the flush lever until the slack looks right. Then flush a few times and make sure the flapper seals every time. This is a two-minute fix and I have seen it solve the problem more than once when the homeowner was about to replace the whole toilet.

Cause 4: A Cracked Overflow Tube

This one is less common but worth knowing about. The overflow tube itself can crack, usually near the base. When it does, tank water drains into the tube below the intended level, so the fill valve keeps running to try to maintain the level.

How to check: Look closely at the overflow tube for a crack, especially near the bottom where it meets the flush valve. You may need to drain the tank to see it.

How to fix: A cracked overflow tube usually means replacing the whole flush valve assembly, which includes the tube. The kit costs about $15 to $20. You shut off the water, disconnect the water line, unscrew the tank bolts, lift the tank off the bowl, and swap the flush valve. It sounds like a lot, but it is a 30-minute job with a wrench and a sponge. If your toilet is old and the tank bolts look corroded, replace them while you are in there.

What NOT to Do

Do not pour drain cleaner or any chemical into the toilet tank. It will destroy the rubber parts and make everything worse. Do not overtighten the tank bolts when you reassemble anything. Porcelain cracks, and a cracked tank means a new toilet. A quarter turn past snug is enough. And do not ignore a running toilet because the water bill is the landlord's problem. If you rent, tell your landlord. A running toilet is a maintenance issue they should fix, and documenting it in writing protects you from getting blamed for the water bill.

How Much This Saves You

A plumber charges $150 to $250 for a service call to fix a running toilet. The parts for every fix in this article cost under $20 combined. The most common fix, the flapper, is under $8 and takes 15 minutes. There is no plumbing job with a better return on your time than this one.

When to Call a Plumber

Be honest with yourself. If you have replaced the flapper and the fill valve, adjusted the chain, checked the overflow tube, and it still runs, the problem might be a hairline crack in the tank or a warped flush valve seat that needs professional attention. Also, if water is leaking onto the floor from anywhere, that can mean a failed wax ring or a cracked base, and those jobs are messier than they look. Knowing when to stop is part of being a good DIYer.