Toilet Running Constantly

Common Symptoms

• Continuous sound of water trickling or running in the toilet
• Water bill is noticeably higher than usual
• Phantom flushes — toilet seems to flush briefly on its own
• Hissing or running sound from the tank between flushes
• Visible water ripples in the toilet bowl when no one is using it

Most Likely Causes

1. 1

   Worn or Warped Flapper (Most Common)

   The rubber flapper seals the drain at the bottom of the tank. Over time, it warps, hardens, or develops mineral buildup that prevents a watertight seal. Water constantly trickles past it into the bowl. This is the #1 cause of running toilets.

2. 2

   Float Set Too High

   The float tells the fill valve when to stop filling the tank. If adjusted too high, the water level rises above the overflow tube and drains continuously — you'll hear constant running even with a good flapper. Bend the float arm down slightly or adjust the float adjustment screw.

3. 3

   Fill Valve Failure

   The fill valve refills the tank after each flush. When it fails, it may not shut off completely, causing a slow constant trickle or hissing sound. Replacing the fill valve is a $10–20 repair.

4. 4

   Damaged Flush Valve Seat

   The flush valve seat is the ring that the flapper presses against to form a seal. If it's cracked or has mineral deposits, even a new flapper won't seal properly. Clean mineral deposits with vinegar, or replace the flush valve if damaged.

Quick DIY Checks

1. 1The food coloring test: add 5–10 drops of food coloring to the toilet tank. Do NOT flush. Wait 15–20 minutes. If color appears in the bowl, water is leaking past the flapper — replace the flapper.
2. 2Remove the tank lid and check the water level. The water should sit about 1 inch below the top of the overflow tube. If water is running into or above the overflow tube, the float is set too high.
3. 3Adjust the float: on a ballcock fill valve, gently bend the float arm downward. On a modern fill valve, turn the float adjustment screw counterclockwise or slide the float clip down. The water level should drop.

1. 4To replace the flapper: turn off the water supply valve behind the toilet, flush to empty the tank, unhook the old flapper from the overflow tube ears, and snap the new one in place. Reconnect the chain (leave 1/2 inch of slack).
2. 5Check the flush valve seat for mineral buildup: run a finger around the inside of the valve seat while the tank is empty. If it feels rough or you see white deposits, scrub with white vinegar and a toothbrush. Replace the flush valve if cracked.

Repair vs Replace

Recommended Tools & Parts

• Toilet Flapper

  The rubber seal at the bottom of the tank. Fits most standard toilets — check your brand for exact fit (Korky and Fluidmaster are universal fits for most).

  $5–$10

  Buy on Amazon →

• Fill Valve Kit

  Replaces the entire fill valve assembly. Fluidmaster 400A fits almost all toilets and solves most fill and running problems.

  $10–$20

  Buy on Amazon →

• Float Ball

  Replacement float for older ballcock-style fill valves. If the float is waterlogged, it won't rise high enough to shut off the water.

  $6–$12

  Buy on Amazon →

• Complete Toilet Repair Kit

  All-in-one kit with flapper, fill valve, and handle. Economical if multiple components need replacing.

  $15–$25

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

Related Repairs