A running toilet isn't just annoying — it's expensive. At 200 gallons per day, a constantly running toilet adds $70–$200 to your annual water bill. The good news: 90% of running toilet problems are caused by three cheap, easy-to-replace parts. You don't need a plumber for this.
Step 1: Diagnose the Problem
Remove the tank lid and set it aside safely. Flush the toilet and watch what happens. You're looking for three things: Does the flapper seal completely after the flush? Does the water level rise to within 1 inch of the overflow tube? Does the fill valve shut off cleanly? Each failure points to a different fix.
- Add a few drops of food coloring to the tank — if color appears in the bowl without flushing, the flapper is leaking
- Water running into the overflow tube means the fill valve float is set too high
Fix 1: Replace the Flapper (Most Common)
The flapper is the rubber seal at the bottom of the tank. It warps, hardens, and develops mineral deposits over time. To replace it: turn off the water supply valve behind the toilet, flush to empty the tank, unhook the old flapper from the overflow tube ears and disconnect the chain from the flush handle arm, snap the new flapper onto the ears and reconnect the chain (leave 1/2 inch of slack), turn the water back on and test.
- Bring the old flapper to the hardware store to match the size — they're not universal
- A flapper costs $5–$15 and takes 5 minutes to replace
- Too much chain slack causes the flapper to not seal; too little causes it to stay open
Fix 2: Adjust or Replace the Fill Valve
If water is running into the overflow tube, the float is set too high. On a ball float (the round ball on an arm), bend the arm slightly downward to lower the water level. On a cup float (a cylinder that slides up and down the fill valve), pinch the clip and slide it down. The water level should sit 1 inch below the top of the overflow tube. If the fill valve is old or damaged, replace the whole unit — they cost $10–$20 and install in 15 minutes.
- The ideal water level is marked inside most tanks with a 'water line' indicator
- Fluidmaster 400A is the most reliable universal fill valve — available at any hardware store
Fix 3: Fix the Flush Handle or Chain
Sometimes the problem is simpler: the chain is tangled, too short, or caught under the flapper. A chain that's too short holds the flapper open; one that's too long gets caught underneath it. Adjust the chain length so there's about 1/2 inch of slack when the flapper is closed. If the handle itself is loose or broken, replacement handles cost $8–$15 and require only a wrench.
- Flush handle nuts are reverse-threaded — turn clockwise to loosen
When to Call a Plumber
Call a professional if: the toilet rocks or the floor around it feels soft (possible wax ring failure or subfloor damage), you see water on the floor that isn't from condensation, the toilet is cracked, or you've replaced all three components and it's still running. These situations go beyond a DIY fix.
Replace All Three Parts at Once
A toilet repair kit with flapper, fill valve, and flush valve costs $20–$30 and takes 30 minutes. If your toilet is more than 10 years old and running, replacing all three components at once is cheaper than making three separate trips to the hardware store over the next few years.
Problem More Serious Than a Running Toilet?
Our licensed plumbers handle everything from leaks and clogs to full bathroom plumbing overhauls.