Why Does My Toilet Keep Running — and What Fixes It?

Why does my toilet keep running after I flush?

Because water is still leaving the tank. It is either slipping past the flapper into the bowl, or the fill valve is not shutting off and the water is pouring down the overflow tube [6][9].

A tank toilet works the same way in almost every bathroom. Press the handle and the chain lifts the flapper at the bottom of the tank; the water drops into the bowl and the flapper falls back onto its seat. Then the fill valve opens and refills the tank, sending a little water through the refill tube into the overflow tube to top up the bowl, until the float rises to the set level and closes the valve [5]. Florida’s plumbing code asks exactly that of the fill device: refill the tank after each flush, then shut the water off completely [10].

A running toilet is one of those two steps failing. Kohler’s troubleshooting guide splits the symptom the same way: water that runs continuously points to the fill valve and the water level, and water that runs sporadically, starting and stopping on its own, points mainly to the flapper, its chain and the seat it closes on [9]. EPA’s WaterSense program names worn-out toilet flappers and malfunctioning fill valves among the common household leaks, and says most toilet leaks come from old or worn-out flappers [2][3].

How can I tell if my toilet is leaking into the bowl?

Put a few drops of food coloring in the tank, do not flush, and look at the bowl after 10 minutes: if any color shows up, the tank is leaking into the bowl [1]. Flush when you are done so the dye does not stain the tank [1].

To narrow it down, Korky — one of the two flapper makers whose repair guides EPA points homeowners to — describes a second check [1][6]. After the tank refills, mark the water level with a pencil, close the stop valve behind the toilet and wait at least 25 minutes. If the level falls below the mark, a part inside the tank is leaking. Leave the water off for a couple of hours and see where the level stops: at the flapper means a new flapper or seal; at a point on the overflow tube or the bottom of the tank means the flush valve itself needs replacing [6].

If the bowl stays clear but you can still hear water, lift the lid and watch the top of the overflow tube. Water running into it means the other path — the water level or the fill valve, covered below. And if you suspect a leak somewhere else in the house, EPA suggests reading the water meter before and after a two-hour period when no water is being used: if it changes at all, you probably have a leak [1].

• Dye in the bowl after 10 minutes → water is getting past the flapper [1]
• Level falls to the flapper with the water off → flapper or flush valve seal [6]
• Level falls to a point on the overflow tube or the tank bottom → flush valve [6]
• Water pouring into the top of the overflow tube → water level or fill valve [6][9]

Why does my toilet refill by itself every few minutes?

Because the tank is slowly losing water to the bowl, and the fill valve is switching on to replace it. Fluidmaster’s instructions put it plainly: a fill valve that turns on and off by itself means the tank is losing water, and the fix is to clean the flapper and the seat it closes on — and, if the leak continues, to change the flush valve [5].

It is easy to blame the fill valve, because that is the part you hear. Korky makes the same point: a fill valve turning on does not always mean it is broken; in most cases a worn flapper or flush valve seal is letting water leak slowly into the bowl, the float drops with the level, and the valve turns the water back on [6]. EPA adds that an old or worn flapper can make a toilet flush on its own, or silently leak thousands of gallons a year [1].

On a two-piece toilet there is one more place the tank can lose water: the gasket where the flush valve passes through the bottom of the tank. Kohler’s fix is to remove the tank and tighten the flush valve nut without over-tightening it, and to replace the gasket if it still leaks [9]. With the tank off the bowl, that is a reasonable point to call a plumber.

How do I know if my toilet flapper is bad?

If dye from the tank reaches the bowl, the flapper — or the seat it closes on — is not sealing [1][6]. Rubber does not last forever: Korky lists well water, hard water, treated municipal water and in-tank cleaning tablets as things that make a rubber flapper deteriorate until it stops sealing [7], and EPA says to check the flapper periodically and replace it at least every five years [1].

Look at the seat as well as the flapper. Korky’s advice is to inspect the flush valve’s sealing surface for debris, mineral deposits or damage: clean the deposits off so the flapper can seal, and replace the flush valve if the seat is cracked or warped [6]. Before a new flapper goes on, Korky says to clean the flush valve of sediment and debris so the new one seals and does not start leaking slowly [7].

It also has to be the right part. The flapper must match the size of the flush valve opening, and tower or canister flush valves take a seal made for that model rather than a flapper [6]. EPA’s tip is to take the old flapper, or a photo of it, to the store, and to check its width and whether it has a foam float that may need replacing too [1]. Fluidmaster’s instructions add a warning about in-tank drop-in bowl cleaners that contain bleach or chlorine: they damage tank components and may cause flooding [5].

Can the flapper chain make a toilet keep running?

Yes. A chain that is too tight holds the flapper off its seat, and one with too much slack can let loose links fall into the drain opening under the flapper — either way the tank cannot seal [6][7].

How much slack is right? Fluidmaster says to clip the chain to the tank lever directly above the flapper and leave about ½ inch of slack [5]; Korky says one to two links [6]. Too loose has its own symptom: the flapper does not open all the way and the flush is slow [7]. Kohler’s guide for a toilet that runs on and off starts in the same place — adjust the chain so the seal is not held off the flush valve seat [9].

If the toilet stops running only when you jiggle the handle, something in that linkage is holding the flapper up: the chain, or a lever arm that is out of line. Kohler’s guide for a toilet that runs continuously includes setting the trip arm bracket and flange parallel with the tank top, where the toilet has them [9].

Why is water running into the overflow tube?

Because the water in the tank is rising to the top of the overflow tube — the level is set too high, or the fill valve is not closing — and the overflow is doing its job by sending the excess into the bowl [6][10]. EPA’s leak-detection guide says a stuck fill valve can waste 4,300 gallons of water a day if it goes unnoticed [3].

The level is set at the fill valve. Fluidmaster recommends a water level ½ inch below the top of the overflow pipe, and Korky gives the same figure [5][8]; many tanks also carry a waterline mark, and Kohler’s guide says to set the level to match it [9]. On the Fluidmaster valve its instructions describe, an adjustment screw raises the level when turned clockwise and lowers it counter-clockwise; other valves use a clip or a float arm, so follow the instructions for yours [5].

If lowering the level does not stop it, the valve itself is not shutting off. Kohler’s next step is to clean debris from the fill valve seat and seal washer or replace the valve, and to replace it if the float sinks [9]. Korky lists the same causes — a float set too high, a valve clogged with debris, or one failing to shut off [6] — and Fluidmaster’s instructions show how to lift the cap off its valve and flush debris out, and say a valve that has been in use for some time, or whose float cup does not drop when the tank is flushed, needs a new seal [5].

Check the refill tube while the lid is off. It should be clipped to the overflow pipe so it pours in from above; Fluidmaster warns against shoving it down the overflow pipe, because that may cause significant water waste [5]. A steady hiss usually belongs here too: Korky’s causes for a hissing toilet are a worn flapper or flush valve seal, a fill valve that is not shutting off fully, or a water level set too high [8].

How high should the fill valve sit above the overflow tube?

High enough that its critical-level mark — the “C.L.” on the valve — sits at least 1 inch above the top of the overflow tube. Fluidmaster’s instructions require it, and the 2023 Florida Building Code, Plumbing requires the fill valve’s backflow preventer to be at least 1 inch above the full opening of the overflow pipe [5][10].

The point is your drinking water. Florida’s code requires every flush tank to have an anti-siphon fill valve conforming to ASSE 1002 or one of the other standards it names [10]. Because the overflow tube caps how high the water in the tank can rise, a backflow preventer at least an inch above its opening stays clear of the tank water; Fluidmaster’s instructions put it simply — code compliance helps protect your home and drinking water supply [5].

On the Fluidmaster valve, setting the top of the valve 3 inches above the overflow pipe puts the C.L. mark in the right place, and the top of the overflow pipe has to be at least 1 inch below the tank lever hole [5]. A fill valve set too low can still fill and shut off normally, so after anyone replaces one, it is worth checking that mark.

Can I fix a running toilet myself, or do I need a plumber?

Often yourself. The flapper and fill valve makers publish step-by-step instructions for exactly these jobs — replacing the flapper, setting the chain, adjusting the water level, and cleaning or replacing the fill valve [5][6][7] — and EPA links homeowners to both companies’ repair guides [1]. Call a plumber when:

• the water level drops to a point on the overflow tube or the bottom of the tank — Korky’s sign that the flush valve itself needs replacing [6]
• a two-piece toilet leaks at the flush valve gasket, which means taking the tank off the bowl [9]
• the stop valve behind the toilet will not close, or leaks when you turn it
• the tank or the overflow tube is cracked
• it still runs after a new flapper, a chain adjustment and a cleaned or replaced fill valve
• there is water on the floor

Is a running toilet an emergency?

Usually not: the overflow tube is there to send extra water into the bowl rather than onto the floor [10]. It still wastes water until it is fixed, so it is worth booking rather than living with.

Water on the floor is different. Close the stop valve behind the toilet — clockwise, as both Fluidmaster’s and Korky’s instructions describe [5][7] — and call. The phone is answered 24/7 by Kate, our AI voice assistant, who records the job; site work is scheduled Monday to Friday, 8am to 6pm.

We install and repair toilets. The two-piece toilet at the top of this page is one we installed on grey tile in Clearwater.

What this means in Clearwater and across Tampa Bay

Korky names hard water and treated municipal water among the things that wear out a rubber flapper, and mineral deposits on the flush valve seat among the things that stop one sealing [6][7]. Utility water around Tampa Bay ranges from soft to very hard depending on which utility supplies you — our article on hardness by utility gives the published numbers. Where the water is hard, look at the seat as well as the flapper when a toilet starts to run, and clean it before a new flapper goes on [7].

We install and repair toilets in Clearwater, Tampa and across Tampa Bay. If the dye test points at the flapper, that is often a homeowner fix; if it points at the flush valve or the seal under the tank, or the toilet keeps running after the simple fixes, call us.

FAQ

Sources

We review and cite. We do not reproduce a paper or a manual — follow the links for the originals.

1. [1]Fix a Leak Week — US Environmental Protection Agency, WaterSense · 2026Government or standards body · dye test: a few drops of food coloring in the tank, color in the bowl after 10 minutes means a leak, flush afterwards; an old or worn flapper can make a toilet flush on its own or silently leak thousands of gallons a year; check the flapper periodically and replace it at least every five years; bring the old flapper or a photo, check width and foam float; meter check over two hours without water use; links Korky’s and Fluidmaster’s repair guides; page last updated March 13, 2026; read 2026-10-11
2. [2]Residential Toilets — US Environmental Protection Agency, WaterSense · 2026Government or standards body · most toilet leaks are due to old or worn-out flappers; a flapper is rubber, plastic or silicone; page last updated May 29, 2026; read 2026-10-11
3. [3]Know Your Flow and Curb Water Waste: A WaterSense Guide to Leak Detection and Flow Monitoring Devices (EPA 832-F-26-001) — US Environmental Protection Agency, WaterSense · February 2026Government or standards body · worn-out toilet flappers and malfunctioning fill valves are common household leaks; a stuck fill valve can waste 4,300 gallons a day if unnoticed; about 20 percent of toilets leak; continuous flow through the fill valve indicates a leaky flapper or other malfunction; read 2026-10-11
4. [4]WaterSense for Kids — US Environmental Protection Agency, WaterSense · 2026Government or standards body · a leaking toilet could be wasting about 200 gallons of water every day — EPA’s figure, given on its page for children; page last updated April 21, 2026; read 2026-10-11
5. [5]Fill Valve & Flapper Installation Instructions (400C, Part 4-757, Grev. 5) — Fluidmaster · 2013Manufacturer's manual · C.L. mark 1 inch above the top of the overflow pipe, top of valve 3 inches above it; overflow top at least 1 inch below the tank lever hole; water level ½ inch below the overflow top; chain clipped above the flapper with ½ inch of slack; refill tube clipped to the overflow, not shoved down it; a fill valve that turns on and off by itself means the tank is losing water; cap removal, debris flushing and seal replacement; no bleach or chlorine drop-in tank cleaners; read 2026-10-11
6. [6]How to Fix a Running Toilet — Korky (Lavelle Industries)Manufacturer's manual · a refilling fill valve usually means a worn flapper or flush valve seal; pencil-mark shut-off test (at least 25 minutes, then a couple of hours); float set too high, debris or a valve failing to shut off; flapper must match the flush valve opening; 1–2 links of chain slack; clean mineral deposits from the seat, replace a cracked or warped flush valve; read 2026-10-11
7. [7]How to Replace a Toilet Flapper — Korky (Lavelle Industries)Manufacturer's manual · well water, hard water, treated municipal water and in-tank cleaning tablets deteriorate rubber flappers; clean the flush valve before fitting a new flapper; chain too loose gives a slow flush, too tight keeps the toilet running; stop valve closes clockwise; read 2026-10-11
8. [8]How to Fix Loud or Broken Fill Valve — Korky (Lavelle Industries)Manufacturer's manual · hissing: worn flapper or flush valve seal, fill valve not shutting off fully, water level too high; set the level ½ inch below the top of the overflow tube; read 2026-10-11
9. [9]Toilet Troubleshooting (1175975-5-B) — Kohler Co. · 2013Manufacturer's manual · water runs continuously vs sporadically; set the tank level to the waterline mark; chain slack so the seal is not held off the seat; trip arm bracket and flange parallel with the tank top; clean the fill valve seat or replace the valve; two-piece toilets: remove the tank and tighten the flush valve nut or replace the gasket; read 2026-10-11
10. [10]2023 Florida Building Code, Plumbing, 8th Edition — §415.3 Flush tanks, §415.3.1 Fill valves, §415.3.2 Overflows in flush tanks — Florida Building Commission / International Code Council · 2023Law / code · the fill device must refill the tank after each flush and shut off completely; antisiphon fill valve to ASSE 1002/ASME A112.1002/CSA B125.12 or CSA B125.3; backflow preventer not less than 1 inch above the full opening of the overflow pipe; overflow discharges to the bowl and is sized to prevent flooding the tank; read 2026-10-11