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How to Fix a Running Toilet (And When to Call Someone)

May 2026 — Handled Home, Moon Township, PA

A running toilet is one of those problems that's easy to ignore because it doesn't seem urgent. The toilet still flushes, nothing is visibly broken, and it's just a little noise. But a toilet that runs constantly can waste hundreds of gallons of water a day, which shows up directly on your water bill every single month. It's worth fixing.

The good news is most running toilets are caused by one of three simple things, and two of them are straightforward DIY fixes that cost almost nothing.

How a Toilet Works — The Quick Version

Understanding why a toilet runs starts with knowing what's happening inside the tank. When you flush, the flapper — a rubber seal at the bottom of the tank — lifts up and lets water rush into the bowl. As the tank empties, a float drops down and opens the fill valve, which refills the tank with fresh water. When the water reaches the right level the float rises, shuts off the fill valve, and the flapper drops back down to seal the tank.

A toilet runs when this cycle doesn't complete properly — either water is leaking past the flapper into the bowl, the fill valve isn't shutting off, or the water level is too high and running into the overflow tube.

Step 1 — Figure Out Which Problem You Have

Take the lid off the tank and look inside while the toilet is running. You're looking for one of three things:

Water trickling into the bowl. If you see or hear a trickle going into the bowl even when nobody has flushed recently, the flapper isn't sealing. This is the most common cause of a running toilet and usually the easiest fix.
The fill valve running constantly. If the fill valve is running but the tank seems to be at a normal level, water is escaping somewhere — usually past a bad flapper.
Water going into the overflow tube. The overflow tube is the tall tube in the middle of the tank. If water is running down into it, the tank is overfilling because either the float is set too high or the fill valve isn't shutting off properly.

Simple test for a leaking flapper: Put a few drops of food coloring in the tank and don't flush for 15 minutes. If color appears in the bowl, the flapper is leaking.

The Three Most Common Causes and How to Fix Them

Cause 1 — Bad Flapper

The flapper is a rubber seal and rubber degrades over time — it warps, hardens, or gets coated with mineral buildup and stops seating properly. This is the cause of most running toilets.

Try this first: Press down on the flapper with your finger while the toilet is running. If the running stops, the flapper isn't sealing and needs to be replaced.

How to fix it: Turn off the water supply valve behind the toilet, flush to empty the tank, unhook the old flapper from the ears on the overflow tube and disconnect the chain from the flush handle arm. Take it to the hardware store to match the size — flappers aren't all universal. Snap the new one on, reconnect the chain with a little slack, turn the water back on, and test. This takes about 10 minutes and costs a few dollars.

One thing to check: Make sure the chain has just a little slack — not too tight and not so loose it bunches up under the flapper. A chain that's too tight holds the flapper open slightly and causes a slow leak even with a new flapper.

Call us if: You replace the flapper and the toilet still runs, or the seat the flapper rests on is visibly cracked or warped. A damaged flush valve seat means the whole flush valve assembly needs replacing, which is a more involved job.

Cause 2 — Float Set Too High

If water is going into the overflow tube, the tank is overfilling. The float — either a ball on an arm or a cylindrical float that slides on the fill valve shaft — controls when the fill valve shuts off. If it's set too high, the water level rises past the overflow tube and drains continuously.

How to fix it: The fix depends on your float type.

For a ball float on an arm: bend the arm down slightly so the ball rides lower, causing the valve to shut off sooner. Some have an adjustment screw instead of bending.
For a cup or cylinder float on a fill valve: there's usually a clip or screw on the side of the fill valve that adjusts the float height. Sliding it down lowers the water level.

The water level should sit about an inch below the top of the overflow tube. Adjust, let the tank refill, and check. Repeat until the fill valve shuts off before water reaches the overflow tube.

Call us if: Adjusting the float doesn't stop the overflow, or the fill valve itself keeps running even with the float in the correct position.

Cause 3 — Worn Fill Valve

If the flapper is fine and the float is set correctly but the toilet still runs, the fill valve itself has worn out and isn't shutting off cleanly. Fill valves are mechanical parts that wear out over time, especially in areas with hard water.

Try this first: Lift up on the float arm or cup while the fill valve is running. If the water stops, the float is the issue. If water keeps running even with the float lifted all the way up, the fill valve is worn out.

How to fix it: Fill valve replacement is a manageable DIY job. Turn off the supply valve, flush to empty the tank, disconnect the supply line under the tank, unscrew the locknut holding the fill valve in from underneath, and lift the old valve out. Install the new one at the correct height, reconnect everything, and turn the water back on. The whole job takes 20–30 minutes. Universal fill valves that fit most toilets are available at any hardware store for under $15.

Call us if: You're not comfortable working under the tank, the supply line connections are corroded and won't budge, or you replace the fill valve and the problem continues.

What If You've Fixed Both and It Still Runs?

If you've replaced the flapper and the fill valve and the toilet is still running, there are a few less common causes worth checking:

Cracked overflow tube. A crack in the overflow tube can let water drain continuously. This requires replacing the flush valve assembly — a bigger job that involves draining the tank completely and replacing the hardware bolted to the tank bottom.

Worn flush valve seat. The seat the flapper rests on can develop mineral deposits or small cracks that prevent a good seal even with a new flapper. Cleaning with vinegar sometimes helps. If the seat is cracked it needs to be replaced.

Float arm or clip failure. Occasionally the float mechanism itself breaks rather than just needing adjustment.

At this point if basic replacement parts haven't solved it, it's worth having someone look at it to determine whether repair still makes sense or whether the toilet itself is old enough that replacement is the better long-term answer.

How Much Water Is a Running Toilet Actually Wasting?

This is worth putting in concrete terms. A slow leak past a worn flapper can waste 30 gallons a day. A medium running toilet wastes around 200 gallons a day. A toilet with water constantly flowing into the overflow tube can waste up to 4,000 gallons a day.

At Pittsburgh-area water rates even a slow leak adds up to real money over a month. A $5 flapper pays for itself in the first few days.

When Toilet Replacement Makes More Sense Than Repair

Most running toilet issues are worth repairing. But a few situations point toward replacement:

The toilet is very old and has had multiple issues. If you're replacing the flapper for the third time in a few years and the fill valve is also going, the toilet is telling you something.
The porcelain is cracked. A crack in the tank or bowl is a replacement situation — cracked porcelain doesn't get better and a tank crack can fail suddenly.
You want to upgrade water efficiency. Older toilets use significantly more water per flush than modern low-flow models. If you're already doing repair work, it's worth pricing out a replacement to see if the water savings make sense.

The Bottom Line

Most running toilets are a flapper or a float adjustment — two fixes that cost almost nothing and take less than 30 minutes. Start there before calling anyone. If those don't solve it, the fill valve is usually next and it's still a straightforward repair.

The one thing not worth doing is ignoring it. A running toilet is silently adding to your water bill every single day until it gets fixed.

If you're in Moon Township, Coraopolis, Sewickley, Robinson, or anywhere in the Pittsburgh area and want someone to just handle it, we offer free estimates. Call or text 412-353-5341 or visit handledhome.net.