Step-by-step fix
Step 1: Shut off water and empty the tank
- Turn the toilet shutoff valve clockwise until the water stops.
- Flush the toilet and hold the handle down to drain as much water from the tank as possible.
- Use a sponge or small cup to remove the remaining water from the bottom of the tank into a bucket.
- Place towels around the base of the toilet and under the supply connection area.
If it works: The tank is mostly empty and you can work without constant dripping.
If it doesn’t: If the shutoff valve does not stop the water, pause the repair until the water can be shut off reliably.
Stop if:- The shutoff valve will not close fully.
- The tank or bowl is already cracked.
- You cannot remove enough water to work safely.
Step 2: Disconnect the supply line and remove the tank
- Place a bucket or pan under the supply line connection beneath the tank.
- Loosen the supply line nut and let any trapped water drain out.
- Remove the tank bolts from inside the tank while holding the nuts underneath if needed.
- Lift the tank straight up and set it on a protected, stable surface.
If it works: The tank is off the bowl and accessible from both sides.
If it doesn’t: If the bolts are stuck, apply steady pressure only. If hardware is badly rusted or spinning in damaged porcelain, stop before forcing it.
Stop if:- A bolt is seized and requires excessive force.
- The porcelain flexes, chips, or cracks.
- You cannot lift the tank safely by yourself.
Step 3: Remove the old flush valve
- Take off the flapper or seal attached to the old flush valve if it is still connected.
- From the underside of the tank, loosen and remove the large flush valve locknut using pliers if needed.
- Lift the old flush valve out from inside the tank.
- Clean the tank opening and sealing surface so the new gasket can sit flat.
If it works: The old flush valve is out and the tank opening is clean and smooth.
If it doesn’t: If mineral buildup or old gasket material remains, clean it off gently before installing the new part.
Stop if:- The tank opening is chipped or cracked.
- The locknut will not move and forcing it may damage the tank.
- The replacement valve does not match the opening or overall size.
Step 4: Install the new flush valve and gasket
- Compare the new toilet flush valve to the old one and confirm the size and mounting style match.
- Insert the new flush valve into the tank opening in the same orientation as the old one.
- Install the gasket and thread on the locknut from underneath according to the part layout.
- Tighten the locknut until snug and secure, but do not overtighten against porcelain.
- Attach the flapper or seal and connect the chain to the trip lever with a little slack.
If it works: The new flush valve sits flat, feels secure, and the flapper moves freely.
If it doesn’t: If the valve rocks, the gasket looks uneven, or the chain is too tight, adjust it now before reinstalling the tank.
Stop if:- The locknut will not thread on smoothly.
- The gasket will not sit flat.
- Tightening causes creaking or stress on the porcelain.
Step 5: Reinstall the tank and reconnect water
- Set the tank back onto the bowl, aligning the bolts and gasket properly.
- Reinstall the tank hardware and tighten each side gradually, alternating so the tank lowers evenly.
- Reconnect the water supply line to the fill valve connection.
- Turn the shutoff valve on slowly and let the tank fill while watching for leaks underneath and around the tank-to-bowl seal.
If it works: The tank fills normally and no water appears around the bolts, supply line, or tank seal.
If it doesn’t: If you see a slow drip, shut the water off and check washer placement, gasket seating, and whether any nut is cross-threaded.
Stop if:- Water leaks steadily from a crack in the tank.
- The tank sits unevenly and will not settle evenly with light tightening.
- A connection must be forced to line up.
Step 6: Test flushing and make final adjustments
- Flush the toilet several times and watch the flapper open, close, and reseat fully.
- Check that the chain has slight slack and does not hold the flapper open.
- Listen for running water after the tank refills.
- Inspect the floor and the underside of the tank again after a few minutes.
If it works: The toilet flushes cleanly, refills, and stops running without leaks.
If it doesn’t: If the toilet keeps running, adjust the chain, confirm the flapper is seated, and recheck that the flush valve is tightened and sealed correctly.
Stop if:- Water continues leaking from the tank opening after rechecking the seal.
- The toilet still runs after basic chain and flapper adjustments.
- You discover a hidden crack or damaged mounting surface.
Replacement Parts
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FAQ
Do I have to remove the toilet tank to replace the flush valve?
Usually yes. On most toilets, the flush valve is secured from the underside of the tank, so the tank needs to come off the bowl for access.
How do I know which toilet flush valve to buy?
Match the valve size and connection style to your old part and tank opening. Comparing the old valve to the new one before installation helps avoid fit problems.
Can I reuse the old gasket or tank bolts?
It is better to replace worn sealing parts while the tank is apart. Old gaskets and corroded hardware are common sources of leaks after reassembly.
Why is my toilet still running after I replaced the flush valve?
The most common causes are a chain that is too tight, a flapper that is not seating flat, or a sealing surface that was not cleaned well before installation.
What if the tank bolts are rusted and will not come out?
Do not force them hard enough to risk cracking the tank. If the hardware is badly seized or the porcelain is under stress, it is safer to stop and have the toilet serviced.