Quick answer: A running toilet is almost always caused by a worn flapper (the rubber seal at the bottom of the tank) or a faulty fill valve. Both are $5–$25 parts you can replace yourself in under 15 minutes — no plumber needed. A running toilet can waste up to 200 gallons of water a day, so it’s worth fixing fast.
This is our complete guide to fixing a running toilet, written by a licensed plumber. It links to the exact replacement parts for each fix.
Step 1: Find Out Why It’s Running
Take the tank lid off and watch. There are three usual culprits:
- Water keeps draining into the bowl → the flapper isn’t sealing. Most common.
- Water keeps running into the overflow tube → the fill valve or float is set too high.
- It runs randomly (“phantom flush”) → a slow flapper leak.
Step 2: Fix a Bad Flapper (the #1 cause)
If water trickles from the tank into the bowl, the flapper has hardened or warped. Shut off the water at the wall valve, flush to empty the tank, unclip the old flapper, and snap in a new one of the same size. See our picks for the best toilet flapper and, if you keep replacing them, read Korky vs Fluidmaster for the longest-lasting option in hard water.
Step 3: Replace a Faulty Fill Valve
If water runs into the overflow tube and never shuts off, the fill valve is worn or set too high. First try lowering the float. If that doesn’t work, swap the valve — it’s a 10-minute job. Here are the best toilet fill valves.
Step 4: Check the Chain, Handle, and Supply Line
A chain that’s too tight holds the flapper open; too loose and it won’t seal. Adjust for a little slack. A sticky flush handle can also hold the flapper up. While you’re in there, a cheap braided supply line is good insurance against leaks.
When to Replace the Whole Mechanism
If the toilet is old and you’re chasing repeated failures, a complete tank repair kit replaces the flapper, fill valve, and overflow in one go — the most reliable long-term fix.
When to Call a Plumber
99% of running toilets are DIY. Call a pro only if the tank is cracked, the toilet rocks at the base (a wax-ring/flange issue, not a running issue), or water is leaking onto the floor.
Related Toilet Repair Guides
- Korky vs Fluidmaster: Which Toilet Parts Should You Buy? (A Plumber’s Verdict)
- Best Bidet Attachments Under $30 in 2026 (Easy Toilet Upgrade)
- Best Toilet Supply Lines in 2026 (Stop Leaks at the Source)
- Best Toilet Tank Repair Kits in 2026 (Fix Everything at Once)
- Best Toilet Handle Replacements in 2026 (Fix a Loose or Broken Handle)
- Best Toilet Plungers in 2026 (What Actually Clears Clogs)
- Best Toilet Wax Ring Replacements in 2026 (Step-by-Step Plumber Guide)
- Best Toilet Seats in 2026 (Easy Upgrade, Big Difference)
FAQ
How much does it cost to fix a running toilet?
Doing it yourself, $5–$25 in parts. A plumber typically charges $75–$200 for the same repair, so DIY saves the most.
Why does my toilet run randomly every few minutes?
That “phantom flush” is a slow flapper leak letting tank water seep into the bowl. Replace the flapper.
Can a running toilet raise my water bill?
Yes — significantly. A bad flapper can waste up to 200 gallons a day, which adds up fast on a metered bill.