How do I replace a toilet flapper or fill valve?

Gather everything before you shut off the water so you are not running to the store mid-job. You need a replacement flapper or fill valve sized to your toilet, an adjustable wrench or channel-lock pliers, a sponge and a small bucket, a towel, and a pair of cleaning gloves. A flashlight helps you see inside the tank.

For parts, match before you buy. Take the old part to the hardware store or note your toilet's brand and model, usually stamped inside the tank lid or on the back wall of the tank. Many flappers and fill valves are sold as universal fits, but some low-flow and pressure-assisted toilets need a model-specific part. Buying the wrong size is the most common reason a repair fails on the first try.

Shut off the water at the valve behind or beneath the toilet by turning it clockwise until it stops. Flush to drain the tank. This is also a good moment to wipe out the scale and grit that Phoenix water leaves on the tank floor.

The flapper is the most common toilet repair. According to Fluidmaster, "the flapper is the leading cause of a leaking or running toilet." A worn flapper is the usual culprit behind a phantom flush, where the tank refills on its own every few minutes because water seeps slowly past the seal. Over time the rubber hardens, warps, or grows a film of mineral scale that keeps it from sealing flat. Follow these steps:

1. 1Shut off the water at the supply valve, then flush and hold the handle to empty the tank as far as it will go.
2. 2Unclip the chain from the flush handle arm so the flapper hangs free.
3. 3Remove the old flapper by sliding its ears off the pins on the sides of the overflow tube, or by unhooking the ring that wraps around the base of the overflow tube. Note how it attaches so you can match the new one.
4. 4Snap on the new flapper the same way, either over the pins or around the overflow tube. Make sure it sits flat and centered over the flush valve opening so it seals.
5. 5Reconnect the chain to the handle arm and set about half an inch of slack. Too tight and the flapper cannot close, so the toilet runs. Too loose and the flapper closes early, giving a weak flush.
6. 6Turn the water back on and let the tank refill.
7. 7Test the flush. Watch that the flapper drops and seals cleanly, and listen for any hissing or refilling that signals the chain or seat still needs adjustment.

If the toilet keeps leaking after a new flapper, the flush valve seat may be pitted with mineral scale. Run a finger around the rim where the flapper lands. A rough or crusty seat will not seal even a new flapper and may need cleaning or a seat replacement. You can often scrub light scale off the seat with a plastic pad and white vinegar, but heavy pitting means the whole flush valve needs to come out. Also confirm the flapper is rated for your flush volume, since some low-flow toilets use a flapper with an adjustable dial that controls how long it stays open.

The fill valve is the tall assembly on the left side of the tank that refills it after a flush. When it fails, the tank may not fill, may overfill and run into the overflow tube, or may make a constant hissing sound. Replacing it takes a few more steps than a flapper because you work with the water supply line:

1. 1Shut off the water, flush to empty the tank, then sponge out the remaining water in the bottom so it does not spill when you disconnect the line.
2. 2Disconnect the supply line from the bottom of the fill valve, which sticks out under the tank. Keep your bucket and towel handy for drips.
3. 3Loosen the locknut that holds the fill valve to the bottom of the tank, then lift the old valve straight out.
4. 4Set the new valve height. Most modern fill valves adjust by twisting or sliding the body. Set it so the top of the valve cap sits about three inches above the overflow tube opening, which keeps the float and shutoff above the water line.
5. 5Install the new valve through the hole, hand-tighten the locknut underneath, then snug it a quarter turn with pliers. Do not overtighten, as that can crack the tank.
6. 6Reconnect the supply line and attach the small refill tube to the overflow tube, clipping it so it points down into the tube, not deep inside it.
7. 7Turn the water back on and set the water level. On most Fluidmaster-style valves, turning the adjustment screw or float clip clockwise raises the level and counterclockwise lowers it. Aim for the marked water line, usually about an inch below the top of the overflow tube.
8. 8Check for leaks at the locknut and supply connection, then flush a few times to confirm the tank fills to the right level and shuts off cleanly.

Sizing comes down to the flush valve opening, the hole in the tank floor that the flapper covers. Measure its diameter. A 2-inch opening is the long-standing standard and takes a standard flapper. Many newer high-efficiency toilets use a 3-inch flush valve for a faster, stronger flush, and those need a 3-inch flapper. A 2-inch flapper on a 3-inch valve will leak constantly, so measure before you buy. Fill valves are more forgiving and most are universal, but pressure-assisted and some specialty toilets still need the matching model.

Phoenix water is the reason these parts wear out faster here. City of Phoenix reports place total hardness around 10 to 17 grains per gallon, which the USGS classifies as hard to very hard. That mineral content leaves scale on the flapper's sealing surface and inside the fill valve, stiffening the rubber and clogging the valve. The damage is far worse if you drop chlorine bleach tablets into the tank. The bleach attacks rubber and plastic, and combined with hard-water scale it can destroy a flapper in months. Fluidmaster sells a hard-water-rated flapper kit for exactly this reason. If you use in-tank tablets, switch to a bowl-only product and expect to replace these parts on a shorter cycle.

These small repairs also save real water. EPA WaterSense reports that household leaks waste nearly 1 trillion gallons nationwide each year, and that the average home leaks more than 9,300 gallons annually, much of it from running toilets. Toilets account for about 30 percent of a home's indoor water use, so a worn flapper that leaks silently can quietly add up on your water bill. To check your flapper seal, run a dye test: put a few drops of food coloring in the tank, wait 10 minutes without flushing, and if color shows up in the bowl, the flapper is leaking and needs replacing.

Most flapper and fill valve swaps are well within DIY range, but a few signs point to a bigger problem. If you replace both parts and the toilet still runs, the flush valve seat or overflow tube may be cracked or scaled beyond cleaning, which means replacing the whole flush valve assembly and pulling the tank off the bowl. That is a longer job many homeowners prefer to hand off.

Call a pro if the supply shutoff valve will not turn or leaks when you touch it, if the tank-to-bowl bolts are corroded, if you see water pooling at the base of the toilet, or if the porcelain is cracked. Water at the base usually points to a failed wax ring rather than a tank part, and a rocking toilet can break that seal and damage the subfloor over time. For a deeper look at chronic running, see our guide on how-to-fix-a-running-toilet, and if the tank fills slowly or not at all, our page on toilet-tank-not-filling walks through the supply-side causes.

HQ Plumbing & Air serves metro Phoenix with 24/7 service. If a simple part swap turns into a leak, a stuck valve, or a tank you cannot reseal, our licensed plumbers can handle it. Call (602) 675-1555.