Why Won't My Toilet Stop Running? 5 Causes and What Each Fix Costs

If you've ever stood in the bathroom at 2 a.m. listening to your toilet hiss like a leaky tire, you already know the feeling. A running toilet isn't just annoying - a single bad flapper can quietly burn through 200 gallons a day, which shows up as a real number on your next water bill.

The good news: nine times out of ten, it's one of five small parts. Here's how to spot which one, and what it actually costs to fix - whether you grab a screwdriver yourself or call someone in.

Not sure where to start? Snap a photo of your tank with Runhome and we'll tell you what part is failing, what it costs, and whether it's a DIY or a pro call - usually in under a minute.

1. A worn-out flapper

This is the #1 culprit. The flapper is the rubber disc at the bottom of the tank that lifts when you flush and drops back down to seal. After a few years it gets stiff, warped, or crusted with mineral scale, and it stops sealing tight. Water trickles into the bowl, the tank refills to compensate, and the cycle never ends.

Quick test: drop a few drops of food coloring into the tank and wait 20 minutes without flushing. If color shows up in the bowl, the flapper is leaking.

What it costs

• DIY: $5–$20 for a new flapper at any hardware store. Five-minute job, no tools.
• Plumber: $50–$100, mostly the service call fee.

2. A fill valve that won't shut off

The fill valve is the tall assembly on the left side of the tank. It refills after a flush and is supposed to click off when the water hits the right level. When it goes bad - usually from sediment or hard-water buildup - it never fully closes, so water keeps dribbling in and overflowing down the center tube.

Quick test: if the water in your tank is sitting at or above the top of the overflow tube, the fill valve isn't doing its job.

What it costs

• DIY: $15–$30 for the part. A little more involved than a flapper, but still a 20–30 minute project for most people.
• Plumber: $159–$325, parts and labor included.

3. A float that's set wrong (or full of water)

The float is what tells the fill valve when to stop. Older toilets have a ball on an arm; newer ones have a cup that slides up the fill valve shaft. If the float sits too high, the tank fills past the overflow tube. If it's a ball, it can crack and slowly fill with water - then it never rises high enough to trigger the shutoff.

Quick test: open the tank and look at the water line. It should rest about an inch below the top of the overflow tube. Higher than that, the float needs to come down.

What it costs

• DIY: Often $0 - most modern floats adjust with a clip or a screw. A replacement ball is under $10. A new float cup typically comes inside a $15–$30 fill valve kit.
• Plumber: Usually rolled into a service call. If they have to swap the fill valve assembly, $159–$325.

Stuck deciding if you should DIY or call a pro? Runhome gives you a side-by-side estimate based on your fixture, your zip code, and what's actually wrong - then we line up a vetted plumber if you want one.

4. Water spilling into the overflow tube

The overflow tube is the vertical pipe in the middle of the tank. It's a safety drain - anything above its rim spills into the bowl instead of onto your bathroom floor. If water is constantly trickling into it, the tube itself isn't broken; something upstream (the float or the fill valve) is the real problem.

Quick test: look down into the tank. Is there a steady stream of water running into the top of the overflow tube? If yes, treat it as a float or fill-valve issue, not an overflow tube issue.

What it costs

• DIY: $0–$30, depending on whether it's an adjustment or a fill valve swap.
• Plumber: $159–$325, again tied to the underlying part.

5. A misaligned refill tube

The refill tube is the skinny flexible hose that clips to the top of the overflow tube. After each flush, it sends a small stream of water down to refill the bowl. If it's pushed too far into the overflow tube (siphoning water down constantly) or clipped on loose, your toilet will keep running.

Quick test: make sure the refill tube ends above the rim of the overflow tube, not below it. The little clip that came with the fill valve is meant to hold it in place.

What it costs

• DIY: Usually $0 - just reposition the clip. A replacement tube is under $5.
• Plumber: $159–$325 if they end up doing a full fill valve replacement.

At-a-glance: cost summary

• Worn flapper is the cheapest and easiest fix, with DIY parts running just $5–$20 versus $50–$100+ for a professional repair.A bad fill valve costs slightly more to DIY at $15–$30, but professional service jumps significantly to $159–$325.
• Float issues are often the most budget-friendly repair, sometimes costing nothing if you only need an adjustment (DIY $0–$10), though a pro visit still runs $159–$325.
• Overflow tube problems can range from a free adjustment to a $30 part for DIYers, while professional repair stays in the $159–$325 range.
• Refill tube position is typically the lowest-cost DIY fix at $0–$5 since it usually just needs repositioning, yet calling a pro still costs $159–$325.
• Across the board, DIY repairs save significantly compared to professional service, with most plumber visits landing in a consistent $159–$325 range regardless of the underlying cause.

When to stop troubleshooting and call a plumber

Most running toilets are a 15-minute fix. But a few situations are worth handing off:

• You've replaced the obvious parts and it's still running.
• You see a hairline crack in the porcelain tank or bowl.
• Multiple toilets in the house are acting up at once (could be water pressure or supply-side).
• The shutoff valve under the toilet is corroded, stuck, or leaking.

In those cases, a pro will diagnose faster than you'll iterate, and most plumbers warranty their work.

The bottom line

A running toilet is one of the cheapest, fastest fixes in your house - and one of the most expensive things to ignore. Most homeowners can solve it for $20 and a Saturday morning. The rest of the time, a plumber gets you sorted under $325.

If you'd rather skip the diagnostic step entirely, that's what we built Runhome for. Send us a quick photo or description, and you'll get:

• An exact diagnosis of which part is failing
• A real cost range for your area
• A clear DIY-vs-pro recommendation
• A vetted plumber lined up if you want one - no callbacks, no estimates by phone

Start a free diagnosis at runhome.com →

Your toilet should be the quietest thing in the house. Let's get it back to that.