How to Replace a Toilet Flush Valve

Step 1: Make sure the flush valve is really the problem

1. Lift the tank lid and flush the toilet once.
2. Watch the water level after the tank refills. If water keeps slipping into the bowl through the valve opening, the flush valve seal or body may be failing.
3. Look for a cracked overflow tube, a damaged valve seat, or mineral buildup that keeps the flapper from sealing.
4. Check that the chain is not too tight and that the fill valve is not overfilling the tank into the overflow tube.

If it works: You have a clear reason to replace the flush valve instead of adjusting the chain or fill valve.

If it doesn’t: If the only issue is chain slack, a worn flapper, or a fill valve that overfills the tank, fix that first before replacing the flush valve.

Step 2: Shut off water and empty the tank

1. Turn the shutoff valve clockwise until the water stops.
2. Flush the toilet and hold the handle down to drain as much water from the tank as possible.
3. Use a sponge or towel to remove the remaining water from the bottom of the tank.
4. Disconnect the water supply line from the bottom of the tank and keep a bucket underneath for drips.

Step 3: Remove the tank and old flush valve

1. Unscrew the tank bolts from underneath while holding the bolt heads inside the tank if needed.
2. Lift the tank straight up and set it on a towel or soft surface.
3. Remove the large flush valve locknut from the underside of the tank using pliers.
4. Pull the old flush valve out from inside the tank.
5. Clean the tank opening and both sealing surfaces so the new gasket can sit flat.

Step 4: Install the new flush valve and tank gasket

1. Insert the new flush valve into the tank opening from inside the tank.
2. Position the overflow tube so it does not interfere with the fill valve or trip lever.
3. Thread the new locknut onto the flush valve from underneath the tank and tighten it snugly so the valve does not shift.
4. Install the tank-to-bowl gasket on the flush valve as directed by the part design.
5. If the replacement kit includes new tank bolts and washers, install them now.

Step 5: Reinstall the tank and reconnect the toilet

1. Set the tank back onto the bowl, guiding the bolts into place evenly.
2. Tighten the tank bolts a little at a time from side to side so the tank lowers evenly onto the gasket.
3. Reconnect the water supply line.
4. Reconnect the flapper or flush mechanism chain to the trip lever with a little slack so it can close fully after each flush.

If it doesn’t: If the tank rocks or sits unevenly, loosen the bolts and reset it before tightening again.

Step 6: Turn the water back on and test the repair in real use

1. Open the shutoff valve slowly and let the tank fill.
2. Watch underneath the tank, around the tank bolts, and around the tank-to-bowl gasket for leaks.
3. Flush several times and make sure the flapper lifts, drops, and seals cleanly.
4. Listen after the tank refills. The water should stop completely and stay off.
5. Check the bowl after 10 to 15 minutes to confirm water is not still leaking from the tank into the bowl.

If it works: The toilet flushes normally, the tank stays dry outside, and the water does not keep running into the bowl.

If it doesn’t: If the toilet still runs into the bowl, recheck chain slack, flapper alignment, and whether the new flush valve is seated flat. If it leaks outside the tank, snug the hardware slightly and test again.