Why toilets run
Inside the tank, the fill valve refills water after a flush and shuts off at a set level. The flapper or flush valve seal holds that water in until the next flush. If the seal leaks, water slips into the bowl and the fill valve turns back on to top it up, which is the hiss or short refill you hear in the middle of the night.
If the fill valve does not shut off fully, water rises until it spills into the overflow tube. Hard water speeds up both problems by roughening seals and gumming up the valve. High house pressure can also keep a fill valve from closing cleanly.
The dye test
Add color
Put a few drops of food coloring in the tank. Do not flush.
Wait
Leave it for at least fifteen minutes without using the toilet.
Check the bowl
Color in the bowl means the flapper or flush seal is leaking.
Check the overflow
If the water level sits above the overflow tube, the fill valve is not shutting off.
Flush and rinse
Flush once to clear the dye so it does not stain.
What the test tells you
- Ifcolor appears in the bowlthe flapper or flush valve seal is worn or warped and usually needs replacing.
- Ifwater runs into the overflowadjust the fill valve height or replace the valve.
- Ifthe tank refills fine but the base is wetthe problem is a supply line, tank bolt or wax seal, not the tank parts; shut off the stop and call a plumber.
- Ifseveral toilets started running at oncehave house pressure tested; the pressure regulator may be failing.
Parts and what they do
| Part | Role | Common failure |
|---|---|---|
| Fill valve | Refills the tank and shuts off at the set level | Will not shut off, or refills slowly |
| Flapper | Seals the flush opening on many toilets | Warped, stiff or covered in scale |
| Flush valve canister | Seals the flush opening on some newer toilets | Worn seal around the base |
| Supply line | Connects the stop valve to the toilet | Drips at the nut or bulges |
| Wax or foam seal | Seals the toilet to the floor drain | Water at the base, odor |
What drives the cost
- Part type
- Many newer toilets use model-specific flush parts rather than universal flappers.
- Stop valve
- A seized stop may need replacing before the tank can be serviced.
- Reset
- Base leaks mean pulling and resetting the toilet.
- Replacement
- A cracked tank or bowl usually means a new toilet.
Questions to ask
- Does my toilet use a standard flapper or a brand-specific flush valve?
- Is the fill valve set at the right water level?
- Should the stop valve and supply line be replaced too?
- Could high house pressure be part of the cause?
Common questions
How much water can a running toilet waste?
It depends on the leak, but even a small continuous leak adds up. Your water meter and bill are the best evidence.
Can I replace a flapper myself?
Many homeowners do. Close the stop, flush to drain the tank and match the part to your toilet. Leave base leaks and stuck stops to a plumber.
Why does the toilet refill on its own at night?
That is the classic sign of a flapper or flush seal leak. Run the dye test to confirm.
General information for Amerige Heights, not a quote or professional advice. In an emergency, call 911.