Inside a toilet tank, two valves do different jobs. The fill valve refills the tank after a flush. The flush valve, which includes the flapper and the seat, releases the stored water into the bowl. People often say they need a new flush valve when the real problem is the flapper, and sometimes the reverse.
How to tell which part is failing
| Symptom | Likely part |
|---|---|
| Toilet runs on and off by itself | Flapper or flush valve seat leaking. |
| Hissing after the tank fills | Fill valve. |
| Weak flush | Flapper closing too early, or clogged rim jets. |
| Water at the base of the tank | Tank-to-bowl gasket or bolts. |
| Handle sticks or feels loose | Chain, lever or handle. |
The dye test
To check for a flush valve leak, add a few drops of food coloring to the tank and wait fifteen minutes without flushing. If color appears in the bowl, water is leaking past the flapper or seat. If not, the leak is likely elsewhere.
Toilet still running after a new flapper?
Call and tell us what you already replaced.
Flapper first, valve second
A worn flapper is the cheapest and most common cause. It warps, hardens or collects grime and no longer seals. Replacing it is a small job. If a new flapper still leaks, the seat it presses on may be pitted or crusted, and the whole flush valve assembly needs to be replaced.
Replacing a flush valve
Shut off and empty the tank
Close the supply, flush and sponge out the water.
Remove the tank
Disconnect the supply and unbolt the tank from the bowl, if it is a two-piece toilet.
Swap the valve
Remove the old assembly and install a matching one with a new seal.
Reassemble
Set the tank back with new gaskets and tighten bolts evenly.
Test
Fill, flush several times and check for drips.
Matching the valve to your toilet matters. Sizes vary, with two-inch and three-inch openings common. Taking a photo of the tank interior to the hardware store helps, and so does reading the model number inside the tank.
When to replace the toilet instead
If the tank is cracked, the china is stained and worn or the toilet has never flushed well, a new toilet may be better than new parts. Our toilet repair page explains how we decide, and plumbing installation covers replacement.
Parts inside a toilet tank, in plain language
| Part | Job | Common failure |
|---|---|---|
| Flapper | Seals the opening at the bottom of the tank | Warps or hardens and leaks. |
| Flush valve seat | The surface the flapper presses against | Pitted or crusted with minerals. |
| Overflow tube | Safety path if the tank overfills | Cracks or an incorrect water level. |
| Fill valve | Refills the tank after each flush | Hisses, runs on or fills slowly. |
| Chain or lever | Lifts the flapper when you flush | Too tight, too loose or tangled. |
Quick checks that save a service call
- Remove the tank lid and look at the water level. It should sit about an inch below the top of the overflow tube.
- Lift the flapper chain slightly to check that it has a little slack, not a tight pull.
- Wipe the flapper edge with your fingers. If it feels slimy or rough, it may not be sealing.
- Press down on the flapper while the toilet is running. If the noise stops, the flapper or seat is the problem.
- Check for mineral crust on the seat and clean it gently with a non-metal pad.
Dual-flush and other newer designs
Dual-flush toilets use a flush valve with two settings, and the parts are more complex. Tower-style canister valves and pressure-assisted systems have their own parts and need their own components. Before you buy anything, look up the model name or take a photo of the inside of the tank.
If you cannot find the model, a plumber can often identify a part from a photo. For a toilet that is old, stained and constantly needing parts, the cost of repairs may approach the cost of a new toilet, and replacement is worth considering.
How much water a leaking flapper wastes
A flapper that leaks lets water trickle from the tank into the bowl, and the fill valve tops up the tank again and again. Because the leak is silent, it can run for weeks. A toilet that cycles on its own every few minutes can waste many gallons a day.
The simplest way to catch it is to listen. Stand by the toilet when the house is quiet. If you hear the fill valve start without anyone touching the handle, you have a leak. The fix is cheap compared with the water it saves.
When to call a plumber
Call if the new flapper still leaks, if the seat is damaged, if the tank bolts spin freely or if the water level will not stay where you set it. Those problems are harder than they look. Our toilet repair page describes how we handle them.
Choosing replacement parts
Universal flush valve kits cover many toilets, but not all. Match the opening size, the overflow tube height and the bolt pattern. Brand-specific parts are best when you can identify the toilet. After you install a new valve, run several flushes and watch the water level to make sure it stops about an inch below the top of the overflow tube.
A running toilet and your Monterey Park water bill
A running toilet can waste a lot of water without making a sound. The City of Monterey Park's Water Division can answer questions about your meter and billing, and a steady rise in a bill with no change in use is a reason to check the toilets first.
Water that flows over scale-crusted parts wears seals faster. The City's 2010 water quality report listed total hardness around 12 grains per gallon, so a flapper in Monterey Park may need replacing sooner than the package suggests. Replacing it once a few years is cheap insurance.
Questions about flush valve repair in Monterey Park
A leak into the bowl points to the flush valve or flapper. A hiss after the tank is full points to the fill valve.
Many people do. The tank bolts and seals need care, because over-tightening can crack the porcelain.
Often a few years, less in hard water.
Yes, it can add noticeably over a month.
Yes, day or night. See toilet repair.
Sources and where to confirm
Local facts and rules on this page rest on the City's 2010 water quality report and the Water Division. Confirm anything that affects your own property with the source.
- City of Monterey Park Water Division, water quality report (2010 edition cited here). Ask the Water Division for the current report.
- City of Monterey Park Water Division, for questions about your meter, billing and the utility side of the line.