Note to readers: This post was updated on July 24, 2026 to reflect current step-by-step troubleshooting and add links to our related toilet repair guides. We refreshed the details below so the advice reflects how we approach this work today.
A toilet that keeps running after you flush isn’t just annoying — it can waste hundreds of gallons of water a day and add up fast on your water bill. Here are the most common causes and what to check before calling a plumber.
1. A Worn Flapper
The flapper is the rubber seal at the bottom of the tank that lifts when you flush and drops back down to seal the tank. Over time it warps, cracks, or stops sealing fully, letting water trickle into the bowl constantly. This is the single most common cause of a running toilet and one of the easiest fixes — flappers are inexpensive and take a few minutes to replace.
2. Fill Valve Issues
The fill valve controls water refilling the tank after a flush. If it’s worn out or misadjusted, it can keep letting water in, or let water run continuously into the overflow tube. Listen for a hissing sound with the lid off — that usually points to the fill valve.
3. Float Set Too High
The float tells the fill valve when to stop. If it’s set too high, water keeps flowing into the overflow tube instead of shutting off. Adjusting the float height (there’s usually a screw or clip) often solves this without replacing any parts.
4. A Cracked Overflow Tube
If water is running down the overflow tube even after adjusting the float, the tube itself may be cracked or too short. This is less common but worth checking if the float adjustment doesn’t fix things.
5. Mineral Buildup or Debris
Hard water deposits and mineral buildup around the flapper seat or fill valve can prevent a proper seal, even with new parts. If your fixtures throughout the house show mineral scale, a whole-house filtration system can reduce this issue across your plumbing, not just the toilet.
6. A Faulty Flush Valve or Handle Chain
A chain that’s too tight can hold the flapper open slightly; too loose and it won’t lift fully. Either way, check the chain length first — it’s the simplest possible fix and easy to overlook.
When It’s More Than a DIY Fix
If you’ve checked the flapper, float, and chain and the toilet is still running, or if you’re dealing with a toilet that won’t flush properly in addition to running, it may be a deeper issue with the flush valve assembly or tank hardware. That’s a quick fix for a plumber and worth doing before the water bill adds up further.
Still running after trying these fixes? Schedule a toilet repair and we’ll have it sorted in one visit.
