Running Toilet: Simple Fixes vs. a Rebuild

Plumbing · 4 min read · By Rodney Jessen · Published October 27, 2026

A toilet that keeps running, or refills on its own in the middle of the night, is one of the most common plumbing calls there is. The good news is that many running toilets come down to one or two inexpensive parts inside the tank. The trick is knowing which part, and when a simple fix has turned into a rebuild.

How the tank works

Lift the tank lid and you will see two main parts. The fill valve is the tall piece on one side that refills the tank after a flush. Its float tells it when to shut off. The flush valve sits in the middle at the bottom. It has a rubber flapper that lifts when you push the handle and drops back down to seal the tank. Next to it is the overflow tube, which sends extra water into the bowl if the tank fills too high.

A running toilet is almost always one of two things: water leaking past the flapper, or water filling so high it spills into the overflow tube.

Quick checks you can do

1. Look at the water level. If water is flowing into the top of the overflow tube, the float is set too high or the fill valve is not shutting off. EPA WaterSense suggests setting the water about an inch below the top of the tube.
2. Try the dye test. Put a few drops of food coloring in the tank and do not flush. If color shows up in the bowl after about ten minutes, water is leaking past the flapper. Flush afterward so the dye does not stain.
3. Check the chain. A chain that is too short holds the flapper open a crack. One that is too long can get caught under it. A little slack is what you want.
4. Listen for hissing. A fill valve that hisses or never fully shuts off is often worn out.

Simple fixes

Many running toilets are fixed with one of these:

• Adjusting the float down so the tank stops filling into the overflow tube.
• Freeing or adjusting the flapper chain.
• Replacing a worn or warped flapper. EPA WaterSense recommends replacing flappers at least every five years. Bring the old one to the store so you get a match for your toilet model.
• Replacing the fill valve if it keeps running after the float is adjusted.

Before you start, turn off the small valve on the wall behind the toilet. If that valve is stuck or drips when you turn it, stop there. Forcing an old shutoff valve can make a small job a wet one.

When it is time for a rebuild

Sometimes a new flapper does not stop the leak. The flush valve seat it sits on may be worn or rough, or the tank parts may simply all be the same age. That is when a rebuild makes sense. A minor rebuild usually means replacing the working parts inside the tank. A major rebuild can mean replacing the flush valve, which often involves taking the tank off the bowl and replacing the gaskets and bolts between them.

A rebuild is worth considering when:

• You have replaced the flapper and the dye test still fails.
• Parts are cracked, corroded, or crumbling when you touch them.
• Water drips from the bolts under the tank.
• You have fixed the same toilet more than once in a short time.

When the problem is at the base

If the toilet rocks, or you see water around the base after a flush, the issue is usually not inside the tank. The toilet may need to be pulled and reset on a new wax ring, which seals the toilet to the drain. Do not ignore it. A slow leak at the base can damage the floor and subfloor long before you see it.

Rules for plumbing work vary by city, so if you are replacing a toilet or changing anything beyond the tank parts, check with your city or Washington L&I.

From our job log

• Seattle, Jun 2026: Minor toilet rebuild.
• Woodinville, Jul 2025: Minor toilet rebuild.
• Seattle, Mar 2025: Major toilet rebuild and reset.
• Sammamish, Jun 2026: Reset a toilet with a new wax ring.

These are real OutToday jobs from our records. No customer names or addresses are shown.

When to call a professional

Call a plumber if the toilet still runs after a new flapper and fill valve, if the shutoff valve is stuck or leaking, if water drips from under the tank, or if the toilet rocks or leaks at the base. Also call if you see stains or soft spots on the floor or the ceiling below a bathroom.

OutToday serves Bellevue and the Eastside. If your toilet will not stop running or you are not sure whether it needs a quick fix or a rebuild, call us at (425) 615-5000 and we will help you sort it out.