How to Replace a Toilet Flush Valve


Replacing a toilet’s flush valve is a straightforward project that can resolve common toilet problems like a weak flush, constant running water, or a stuck valve. With a few tools and a replacement kit, you can swap out the valve in less than an hour.

A flush valve controls the flow of water into the toilet bowl in order to flush away waste. Over time, flush valves can deteriorate, causing leaks or other issues. Replacing the valve restores full flushing power and eliminates leaks.

This guide will walk through the entire process of replacing a toilet flush valve, from turning off the water supply to installing the new valve and adjusting it for optimal performance. With these step-by-step instructions, you can avoid calling a plumber and take care of this common toilet repair yourself.

What You’ll Need

Before getting started, make sure you have the necessary supplies:

  • Replacement flush valve kit (Fluidmaster 400A is a popular universal kit)
  • Adjustable wrench
  • Rag or small bucket
  • Flashlight (optional)

Turning Off the Water

The first step is to turn off the water supply to the toilet:

  • Locate the water supply valve behind or near the toilet. It will likely be close to the wall.
  • Turn the valve clockwise to shut off water to the toilet.

With the water off, you can proceed to replacing the flush valve without water spraying everywhere.

Draining the Toilet Tank

Before removing the old flush valve, you need to drain the water from the tank:

  • Flush the toilet to empty as much water as possible.
  • Use a rag or small bucket to remove any remaining water in the tank.
  • Use a flashlight to see if water remains in the overflow tube. Drain any excess water here.

With the tank empty, you can clearly see the flush valve and remove it.

Removing the Old Flush Valve

Most flush valves twist off by turning counterclockwise:

  • Locate the locknut at the base of the flush valve inside the tank. Plastic valves have a ring you twist off; brass valves have a locknut you unscrew.
  • Twist the ring or locknut counterclockwise. It may be stuck from mineral deposits. Try rocking it back and forth while twisting.
  • Pull up on the valve once the locknut is loosened. The valve should detach from the tank.
  • Remove any washers or gaskets remaining on the flush valve seat.

Installing the New Flush Valve

Follow the instructions included with your replacement kit, but the process is generally:

  • Place a new gasket in the flush valve seat.
  • Insert the new valve through the tank hole.
  • Tighten the locknut clockwise to hold it in place. Do not overtighten.
  • Connect the water supply line to the valve. Hand tightening is sufficient.

Make sure all washers are in the proper order to prevent leaks.

Adjusting the Flush Valve

Once secured, adjust the new flush valve:

  • Turn the water supply back on and let the tank fill.
  • The valve may need adjustment to achieve the right water level in the tank and a proper flush.
  • Twist the adjustment rod on top of the valve to fine tune the water level.
  • Flush the toilet a few times and make any necessary adjustments.


If you encounter any problems after replacing the flush valve, here are some steps to try:

  • Make sure the water supply is fully on. A low water level indicates an insufficient water flow.
  • Check for leaks at fittings and washers. Tighten connections or rearrange washers if needed.
  • Clean valve seals and flush valve seat. Scale buildup can prevent a good seal.
  • Adjust water level again. An improper water level can weaken flushing power.

Replacing a faulty toilet flush valve is usually a quick fix to improve flushing and eliminate running water. With the right parts and these step-by-step instructions, you can avoid the hassle and cost of a plumber to handle this common toilet repair.

How to Replace a Toilet Flush Valve

Supplies Needed

  • Adjustable wrench
  • Replacement flush valve kit (fluidmaster 400A or compatible)
  • Bucket
  • Flashlight
  • Rag

Step 1: Turn Off the Water Supply

Locate the water supply valve behind or near the toilet. Turn it clockwise to shut off the water.

Step 2: Drain the Toilet Tank

Flush the toilet to drain most of the water. Use a rag or small bucket to remove any remaining water. Also drain any water in the overflow tube.

Step 3: Remove the Old Flush Valve

Twist the locknut counterclockwise and pull up on the valve to detach it. Remove any old gaskets or washers.

Step 4: Install the New Flush Valve

Place a new gasket on the flush valve seat. Insert new valve and tighten locknut. Connect supply line.

Step 5: Adjust the Flush Valve

Turn water on and adjust rod to set tank water level. Flush several times and tweak as needed.

Step 6: Troubleshoot Issues

Check water supply, fittings, valve seals if issues like leaks occur. Adjust water level again if needed.

Frequently Asked Questions About Replacing a Toilet Flush Valve

  1. Why does my toilet need a new flush valve?

The most common reasons to replace a flush valve are a weak or sluggish flush, the valve sticking open and allowing water to run constantly, or water leaking from the valve seal. A new flush valve restores proper flushing power.

  1. How do I know which flush valve to buy?

Look for a universal or direct replacement valve made for your brand of toilet. The Fluidmaster 400A fits most toilets and is an economical option. Make sure to purchase the complete kit with all washers.

  1. Do I need any special skills or tools?

Replacing a flush valve is a straightforward project for a DIY homeowner. You’ll need an adjustable wrench and possibly a bucket and flashlight. No plumbing experience is required.

  1. How do I remove the old flush valve?

Start by shutting off the toilet’s water supply. Twist and lift out the old valve after removing the locknut by turning it counterclockwise. Use a rocking motion if it’s stuck.

  1. Where is my water supply valve?

The valve that shuts off water to the toilet is usually located behind the toilet, close to the wall. It’s on the water supply line coming out of the wall.

  1. How do I install the new flush valve correctly?

Carefully follow the manufacturer’s instructions. Usually you’ll install a gasket on the flush valve seat, insert new valve through hole, tighten locknut, and connect water supply.

  1. Why does my new flush seem weak?

Make sure you have sufficient water flow to the valve. Adjust the valve per instructions to raise the water level in tank if needed. Flush several times to let valve seat properly.

  1. What if my flush valve leaks?

Check washers and gaskets and make sure they’re properly seated. Tighten any loose fittings. Hard water deposits on valve seals can prevent a good seal and cause leaks.

  1. How can I make my flush more powerful?

Adjust the water level higher via the valve float rod. Make sure the water supply valve is fully open. Remove any obstructions in the toilet bowl. Consider installing a higher performance flush valve.

  1. Is it easy to adjust a flush valve?

Yes, valves come with simple screw or rod adjustments to fine tune the water level and flow. Make small turns until it flushes properly. Read instructions.


Replacing a faulty or outdated toilet flush valve is one of the handiest repairs a homeowner can perform. Following the steps here to remove the old valve, install an improved replacement valve, and adjust it for optimal flushing can restore full toilet performance. A little time spent on this straightforward toilet repair prevents the nuisance of forever jiggling a toilet handle or constantly running water. With the right flush valve and a little DIY spirit, you can resolve most toilet troubles quickly and easily.