A toilet that runs on its own is almost always leaking water from the tank into the bowl, or the fill valve cannot shut off. Lift the tank lid, drop in a few drops of food coloring and wait ten minutes. Color in the bowl means a bad flapper. No color but constant filling points to the fill valve or float. Both are inexpensive parts.
The sections below walk through each cause, the fix, what cost guides report, and the sign that the problem is not the tank at all.
The Ten-Minute Dye Test
The EPA's WaterSense program recommends a dye test for finding silent leaks. Put a dye tablet or a few drops of food coloring into the tank. Do not flush. Wait ten minutes. If any color shows up in the bowl, water is slipping past the flapper.
This matters more than it sounds. WaterSense says the average household leaks more than 9,300 gallons a year, and nine percent of homes leak 50 gallons or more per day. A toilet is one of the most common sources.
| What you see | What it means | Next step |
|---|---|---|
| Color appears in the bowl. | Flapper or flush valve seat is leaking. | Replace the flapper, check the seat for pitting. |
| No color, water hisses or refills often. | Fill valve not sealing or float too high. | Adjust the float, then replace the fill valve if needed. |
| No color, water runs down the overflow tube. | Water level set too high. | Lower the float until the level sits below the tube top. |
| Water around the base, no running sound. | Wax ring or closet bolts, not the tank. | See the wax ring section below. |
Flapper Trouble: The Usual Culprit
The flapper is the rubber stopper at the bottom of the tank. It lifts when you flush and drops back to seal the opening. Over time the rubber hardens, warps or collects mineral film, and it stops sealing. A chain that is too short, too tight or caught under the flapper can keep it from closing too.
WaterSense advises replacing flappers at least every five years. If yours is older, replace it before you spend time on anything else. Turn the shutoff valve behind the toilet clockwise, flush to empty the tank, unclip the old flapper from its pegs and fit one that matches. Leave a little slack in the chain, about the width of a finger.
Wipe the valve seat with a cloth while the tank is empty. A rough or crusty seat can leak even with a new flapper.
If the dye test is clear and the tank keeps refilling, call a licensed plumber to look at the fill valve.
Call (503) 974-3329Fill Valve and Float Problems
The fill valve is the tall assembly on the left or right of the tank. It lets water in after a flush and shuts off when the float rises to a set level. When the valve wears out, the seal inside no longer closes fully. You hear a faint hiss or the tank tops up every few minutes.
Start with the float. On a cup-style float, squeeze the clip and slide it down the rod a half inch. On an arm-style float, bend or turn the adjustment screw so the ball rides lower. The water line should sit about an inch below the top of the overflow tube.
If lowering the float does nothing, the valve itself has failed. Universal replacement kits need only pliers and a bucket. Turn off the water, drain the tank, loosen the supply nut, swap the valve and reconnect. Check the nut for leaks with dry tissue after you turn the water back on.
Phantom Flushes and the Meter Check
A toilet that restarts by itself every few minutes, a phantom flush, is a flapper leak small enough that the tank slowly drains. The dye test often misses it if you wait too short a time. Leave the dye in for a few hours or overnight when in doubt.
If you suspect leaks but cannot find one, WaterSense suggests reading your water meter before and after a two-hour stretch when nobody uses water. If the dial moves, something is leaking. It could be a toilet, a hose bib or a pipe, and leak detection work can trace the hidden ones. A family of four using more than 12,000 gallons in a colder month may have serious leaks.
What Fixing It Usually Costs
According to HomeGuide, valve or flapper work runs $70 to $150 plus a service call of $50 to $200. For Portland, Angi lists running-toilet repair at $110 to $425. A wax ring job runs about $55 to $230.
| Job | Reported range | Source |
|---|---|---|
| Valve or flapper work. | $70 to $150 | HomeGuide. |
| Service call added | $50 to $200 | HomeGuide. |
| Running toilet repair, Portland. | $110 to $425 | Angi. |
| Wax ring replacement | $55 to $230 | Cost guides. |
These are typical figures and your price will differ. A plumber who sees the toilet can tell you whether it needs a part or a replacement. We state the price clearly before work starts. Our toilet repair service covers flappers, fill valves and seals.
When It Is the Wax Ring Instead
Not every wet toilet is running. A wax ring is the seal between the toilet and the floor flange. If it fails, water or sewer smell escapes at the base, and the toilet may rock slightly when you sit. You may see a stain on the ceiling below or a soft spot in the floor.
The tank can be fine here, and a dye test will show nothing. Wet floor around the base after flushing is the sign.
Replacing the ring means shutting off the water, emptying the tank, disconnecting the supply, lifting the toilet off, scraping the old wax and setting the toilet on a new ring. It is heavy, awkward work. Because of the weight and the risk of cracking the porcelain, many owners hand this one off.
The Rebate for a Replacement Toilet
If the toilet is old, cracked or constantly troublesome, replacement may be the better money. The City of Forest Grove gives a $75 rebate for a WaterSense toilet, which means 1.28 gallons per flush or less. You must be a City water customer, the limit is two per household for life, and you apply within 60 days of purchase.
Check current terms before you buy. Repairing or replacing a toilet that is not concealed in a wall does not need a plumbing permit under Oregon Building Codes Division guidance.
Cornelius and Banks: Same Parts, Different Water Bills
A running toilet looks the same everywhere, but what it costs you depends on your water supply. In Cornelius, water comes through the City of Hillsboro to Cornelius Public Works, and the owner is responsible from the meter to the house. A leak on your side shows up on your bill.
In Banks, the City runs its own water department, and some rural homes use private wells. A well owner is responsible for the well and pump. A running toilet on a well makes the pump cycle more, so it can waste power as well as water. Call (503) 974-3329 if you cannot find the leak.
Forest Grove Note: City Water, Dye Tablets and Shutoffs
Forest Grove customers on City water can get dye tablets from the City for the leak test above, and the $75 WaterSense toilet rebate applies to those same customers. The City's water comes from its Clear Creek Watershed and from Joint Water Commission supply.
If a leak needs the whole house shut off, use the main valve at the house. City policy is that customers and contractors never turn the water off at the city meter. Call Public Works at 503-992-3258 and the City will do it, with no fee in business hours and a fee after hours. If a meter or line breaks after someone shuts it, repairs fall on the homeowner.