The flush valve controls the release of water from the toilet tank into the bowl during flushing. When this assembly becomes worn or damaged, the toilet may run continuously, leak into the bowl, or flush poorly.
Replacing a flush valve restores proper performance for these kinds of flushing issues. Although the repair requires removing the toilet tank on a two-piece toilet, most homeowners can complete the job with basic tools and careful handling. Start by confirming the symptoms below, then follow the steps to replace the flush valve safely.
Quick Answer
A failed flush valve allows water to leak from the tank into the bowl, often causing a running toilet. Replacing the flush valve assembly restores proper sealing and flushing performance.
Common Signs of a Failed Flush Valve
- Toilet runs continuously even after replacing the flapper
- Water leaks steadily into the bowl
- Weak or incomplete flushing
- Visible deterioration around the flush valve seat
- Persistent tank leaks after component adjustments
Likely Causes
Flush valves typically fail due to:
- Aging plastic components
- Mineral buildup or corrosion
- Warped or damaged valve seat
- Overtightened tank hardware
- Long-term wear from repeated flushing
Tools & Materials
You may need:
- Replacement flush valve kit
- Adjustable wrench or channel-lock pliers
- Screwdriver
- Sponge or towels
- Bucket
- New tank-to-bowl gasket (usually included)
- Rubber gloves
Have towels ready to catch remaining water when removing the tank.
Step-by-Step: How to Replace a Toilet Flush Valve
1. Shut Off Water and Empty the Tank
Turn the water supply valve clockwise to stop water flow.
Flush the toilet and hold the handle down to empty the tank. Remove remaining water using a sponge or towel.
Disconnect the water supply line from the tank.
2. Remove the Toilet Tank (2-piece toilet)
Unscrew the tank mounting bolts located at the bottom of the tank.
Lift the tank straight up and place it carefully on a protected surface.
Remove the old tank-to-bowl gasket from the flush valve outlet.
3. Remove the Old Flush Valve
Inside the tank, disconnect the flapper chain if attached.
Loosen the large retaining nut beneath the tank that secures the flush valve assembly.
Lift the flush valve out of the tank opening.
Clean the tank surface thoroughly before installing the new valve.
4. Install the New Flush Valve
Insert the new flush valve through the tank opening.
Install and tighten the retaining nut from beneath the tank. Tighten firmly by hand, then snug slightly with pliers.
Avoid over-tightening, which can crack the tank.
Attach the new tank-to-bowl gasket supplied with the kit.
5. Reinstall the Tank
Position the tank back onto the bowl, aligning mounting holes carefully.
Insert tank bolts and tighten evenly from side to side until the tank sits level and stable.
Do not over-tighten porcelain components.
6. Reconnect Water and Test
Reconnect the supply line and turn the water back on.
Allow the tank to fill and flush several times while checking for leaks at all connections.
Confirm the flapper seals properly and the toilet stops running after refilling.
When the Problem May Be More Serious
Flush valve replacement may not resolve problems if you find:
- Cracked toilet tank
- Severely corroded mounting hardware
- Damaged tank mounting surfaces
- Persistent leaks between tank and bowl
In these cases, replacing the toilet may be more practical than further repair. See Repairing vs Replacing a Toilet.
Preventing Future Flush Valve Problems
- Avoid over-tightening internal components
- Replace aging flappers before leakage develops
- Clean mineral deposits periodically
- Avoid chemical tank cleaners that degrade plastic parts
To Hire a Plumber…
If the repair turns out to be more complicated than expected, you can always find a plumber near you.
For hiring advice, see Trade Secrets for Hiring the Right Plumber.
Related Articles
If you’re not sure what’s causing the problem, see our
Toilet Repair and Troubleshooting Guide for a complete diagnostic overview.
Also see:
