How to fix a running toilet: flapper and fill valve repair
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A four-minute captioned animation explaining gravity-toilet diagnosis, the dye test, free adjustments, matched flapper replacement, fill-valve replacement and final leak checks. No audio; instructions appear on screen. Pause as needed. A schematic gravity-tank overview; not a model-specific installation demonstration.
Before you begin
An accessible standard gravity toilet with an internal running-water problem, sound porcelain and a supply stop that closes gently and reliably.
- The supply stop will not close gently, begins leaking, or water continues entering with it closed.
- You find cracked porcelain, a damaged flush-valve seat or overflow tube, or an external leak.
- The bowl is rising, sewage is present, or water reaches electrical equipment.
- Hardware is inaccessible, corroded or requires force; the exact model or part fit is uncertain.
Follow your exact equipment instructions and any product label. This video summarizes the guide; it does not replace model-specific directions.
Chapters and complete transcript
Use “Jump to a chapter” or the player’s timeline to start at the displayed time. Times in the animation are compressed; the dye test still requires a real ten-minute wait.
Start with the water path
A running toilet can overfill or lose water through its outlet seal. Diagnose first; do not replace both parts by default.
This captioned animation explains a common gravity tank. Pause any step and use your exact model instructions.
Know when to stop
Stop for cracked porcelain, external leaks, a rising bowl or a shutoff that will not close gently. Never force a valve or corroded connection.
Pressure-assisted vessels, concealed and powered toilets need their own service instructions.
Meet the parts
The fill valve and float admit water and shut it off. The flapper and chain release water into the bowl.
The upright overflow tube carries excess water. The small refill hose restores the bowl level during refill.
Overfilling or ghost flushing?
Watch one complete refill with the lid safely on a towel. Water spilling over the overflow rim points to overfilling.
Random refill cycles can mean an outlet leak. A noisy fill valve may be replacing water lost through a bad seal.
The ten-minute dye test
First rule out water spilling into the overflow. Add a few drops of food coloring to the tank, not the bowl.
Wait 10 minutes without flushing. Color in the bowl shows tank water is escaping. Flush out the dye afterward. This animation compresses the wait.
Try the free fixes
Free a snagged chain and a blocked float. Let the flapper rest flat with slight chain slack; follow its instructions.
Secure the loose chain tail. Set the marked tank waterline. Clip the refill hose above an open overflow rim; do not tuck it inside.
Match the replacement
Photograph the tank, model number and old parts. Match the outlet size, mounting style and flush volume. Universal does not mean every toilet.
A canister or tower needs its exact sealing ring and release procedure; do not fit a hinged flapper to it.
Path A: isolate and drain
Choose the flapper path for an outlet leak that adjustment or cleaning did not fix. Close a working supply stop gently.
Flush and hold the handle to drain the tank. Confirm no new water enters. Photograph the chain and hinges before removing the old flapper.
Fit the matched flapper
Unclip the chain and release the flapper by its intended mounting method. Wipe the seat with a soft damp cloth. Stop for cracks or damage.
Fit the matched part and its specified adjustment. No sanding, grease, glue or sealant. Set slight chain slack and check free lift and return.
Path B: confirm inlet failure
Choose this path when the inlet will not shut off after float adjustment, with an outlet leak ruled out.
Use model-approved maintenance first when supported. Never open a valve cap with water on. Replace a cracked or persistently failing valve.
Drain and disconnect
Read the new valve instructions. Close the supply, flush and sponge the tank dry. Confirm no water enters; place towels and a bucket below.
Disconnect the supply coupling without twisting the wall pipe. Support the valve, remove its separate mounting nut, then lift it and its old washer out.
Height and washer matter
Wipe and inspect the mounting hole. Fit the supplied washer in its instructed orientation. Set and lock valve height; check float and lid clearance.
Follow the critical-level requirement. On Fluidmaster 400A-style valves, the C.L. mark is at least 1 inch above the overflow rim. The cap is not that mark.
Mount and reconnect
Seat the valve and fit its mounting nut exactly as directed. Many plastic nuts are hand-tighten only; extra force can damage the tank.
Reconnect an undamaged compatible supply connector by hand to avoid cross-threading. Standard washer-sealed connections need no thread tape or pipe dope.
Clip the refill hose
For an open overflow tube, use the supplied clip above the rim. Aim the stream into the opening; keep the hose end out of tank water.
Do not push the hose down inside: it can siphon. Keep it clear of the float. A dedicated canister port uses its own connection method.
Restore water slowly
Open the supply slowly and watch every disturbed connection. Shut it off if anything drips. Set the tank to its specified waterline.
Confirm complete inlet shutoff below the overflow rim. Set any bowl-refill control by its instructions. Do not alter the overflow to make a valve fit.
Quiet. Dry. Repeatable.
Flush two or three times, letting the tank refill fully. Check free movement, normal bowl refill and complete shutoff.
Use dry tissue on connections, repeat the dye test and recheck later that day. If leaks persist, isolate safely and call. Keep your model and repair photos.