How to Repair a Fluidmaster Toilet Fill Valve


A toilet fill valve is an important component of the toilet tank that controls the water flow into the tank. It’s often referred to as the “ballcock” and uses a float ball on an arm to regulate when water should enter and shut off. Over time, fill valves can develop leaks or fail to shut off properly leading to wasted water. Thankfully, repairing or replacing a fill valve is an easy DIY project that most homeowners can tackle themselves.

The Fluidmaster brand is one of the most popular for toilet components, and their Fill Valves are commonly found in many household toilets. If you have a leaky or malfunctioning Fluidmaster Fill Valve, this guide will walk through the steps to replace it with a new one. We’ll cover how to diagnose problems, drain the tank, remove the old valve, install the new one, adjust the water level, and test it out. With a little time and effort, you can have your toilet working like new again!

How Do Toilet Fill Valves Work?

Before diving into a repair, it helps to understand how a fill valve operates:

  • The main components are the valve body, float cup, and refill tube.
  • When the toilet is flushed, the tank empties and the float drops down with the water level. This opens the fill valve inlet and allows water from the supply line to refill the tank.
  • As the tank fills, the float rises back up. At a preset level, the float arm closes the fill valve to stop the water flow. This adjusts the tank water level.
  • The refill tube replenishes a small amount of water in the toilet bowl after the flush. The tube draws water from inside the tank as it refills.
  • Rubber washers create a watertight seal. The valve inlet has a washer that seals against the water supply line. The tank connection has a washer that seals against the overflow tube.
  • Adjustable components control the water level by stopping the fill valve at different heights. Adjusting the float cup changes when it shuts off the water flow.

Diagnosing Toilet Fill Valve Problems

Some common signs that a fill valve needs repair or replacement include:

  • Running Water – If you hear water running in the tank for extended periods after flushing, the fill valve is likely not shutting off properly. This wastes water.
  • Low Water Level – If the tank doesn’t fill fully before the valve shuts off, the float might be set too low. This can lead to a weak flush.
  • High Water Level – If water in the tank is reaching overflowing, the float might be set too high. Water will go down the overflow tube, wasting water.
  • Water Leaking – Drips near the valve body indicate worn washers. Leaks near tank bolts can mean a bad seal. Refill tube leaks also occur over time.
  • Odd Noises – Hissing, whistling, or chattering can indicate excessive water pressure on a worn valve. Knocking or hammering could mean a loose tank bolt.
  • Failed Flush – A low tank level or leaky valve prevents enough water from filling the bowl to flush waste down.
  • Loose Parts – If the flush is weak, the valve might be loose and not sealing right. Gravity helps pull the valve open for refilling.

If you notice any of these warning signs, inspect the fill valve further to diagnose the issue.

How to Drain the Toilet Tank

Before replacing the fill valve, you need to shut off the water supply and drain out any water left in the tank:

  • Turn off the supply valve behind the toilet to shut off the incoming water. This valve looks like a smaller version of a faucet handle. Turn it clockwise to turn it off.
  • Flush the toilet to empty any water in the tank down into the bowl. The tank needs to be fully empty.
  • Use a sponge to soak up any remaining puddles of water in the bottom of the tank.
  • Place towels around the base of the toilet to catch any additional drips.

Also inspect the rest of the tank components while it’s empty:

  • Check the flapper valve at the bottom of the tank that lifts up to flush water into the bowl. Make sure it’s in good condition and seals tightly over the flush valve opening when shut.
  • Examine the tank bolts holding the tank to the toilet. Look for corrosion and loose nuts that need tightening.
  • Remove the lid and set it aside. Check for any cracks, warps, or damage on the underside.

With the tank fully drained, you’re ready to remove the old fill valve.

Removing the Existing Toilet Fill Valve

Taking out the faulty fill valve takes just a few minutes:

  1. Disconnect the water supply line from the valve. Unscrew the coupling nut that connects the supply line to the fill valve. You’ll likely need channel-lock pliers or an adjustable wrench to loosen it up.
  2. Remove the lock nut holding the fill valve down. Turn it counter-clockwise with pliers to loosen it. Lift the fill valve up and off of the tank opening.
  3. Extract the plastic refill tube from the overflow tube. This piece slides inside the overflow to add water back into the bowl. Gently pull and wiggle it to detach it.
  4. Clean any grime, minerals, or scale off of the valve seat at the bottom of the overflow tube. Buildup here can prevent a good seal with the new valve.
  5. Inspect the rubber tank gasket around the opening. Replace it if it’s dry, cracked, or doesn’t lay flat. A good gasket ensures no leaks.

Now the old fill valve is fully removed and the tank opening is prepped and ready for the new replacement valve.

Installing the New Fluidmaster Fill Valve

Replacing the fill valve is easy. Just follow these steps:

  1. Get your new Fluidmaster 400A or 400AH High Performance Fill Valve. Verify it’s the correct length for your toilet tank by holding it in place before attaching anything.
  2. Slide the cone-shaped gasket piece over the new valve shank. It should fit snugly in place about 2 inches down. This seals the tank opening.
  3. Lower the fill valve into the tank opening. The gasket should rest inside the opening.
  4. Reach underneath inside the tank and screw on the lock nut over the shank. Tighten it by hand until snug.
  5. Connect the water supply line to the valve inlet. Hand tighten the coupling nut. You may need pliers to finish tightening, but be careful not to crack the plastic.
  6. Attach the refill tube back into the overflow tube the same way the old one was inserted. Position the clip on the end a few inches down inside the overflow tube.

The fill valve is now installed! Next you need to adjust it to the proper water level.

Adjusting the Toilet Fill Valve Water Level

Setting the right water level is key to getting a full flush volume and not wasting excess water. Here are the steps:

  1. Turn the water supply back on slowly. Let the tank fill and observe where the water level ends up. Shut the supply back off if it gets too high.
  2. Read the water level indicator on the side of the valve body. Loosen the adjustment nut right underneath this.
  3. Twist the float cup up or down to adjust the water level. Counterclockwise raises the level, clockwise lowers it. Go slowly.
  4. Keep checking by turning the supply back on and letting the tank fill. Repeat the adjustment as needed until the water level is about 1⁄2″-1″ below the tank overflow opening.
  5. When at the right level, tighten the adjustment nut lock to hold the float cup in place.

The new fill valve is ready for action! Turn the main supply back on fully. Test flushing the toilet a few times to make sure it operates smoothly. Also check for any leaks around the tank bolts or supply line connection and tighten if needed. Enjoy your efficiently flushing toilet once again!

Troubleshooting Common Fluidmaster Fill Valve Problems

Even with a new fill valve, issues can still pop up. Here are some common troubleshooting points:

Low water level:

  • Float cup adjusted too low – Twist upward
  • Incorrect fill valve size – Verify correct length for toilet model
  • Kinked refill tube – Straighten tube
  • Low water pressure – Check supply valve fully open

High water level:

  • Float cup set too high – Twist downward
  • Warped float ball – Replace fill valve
  • Float ball waterlogged – Replace fill valve
  • Float arm caught – Reposition against rod


  • Debris under valve seat – Clean valve opening
  • Worn inlet washer – Replace washer
  • Cracked valve body – Replace fill valve
  • Bad adjustment nut seal – Tighten nut

Poor flush:

  • Low tank level – Adjust float higher
  • Sediment buildup – Flush to clean tank and jets
  • Weak trapway flush – May need toilet auger

Noisy operation:

  • Water hammer in pipes – Install water hammer arrestor
  • High water pressure – Use pressure reducing valve
  • Loose fill valve nut – Tighten nut

Constantly sticks open:

  • Malfunctioning float – Replace fill valve
  • Float arm stuck – Reposition arm
  • Float setting too high – Adjust lower

A little troubleshooting can resolve most common issues that come up. But if problems persist, replacing the entire fill valve may be needed.

FAQ About Fluidmaster Fill Valves

Here are answers to some frequently asked questions about Fluidmaster Fill Valves:

Q: How do I know which Fluidmaster valve model to use as a replacement?

A: Check inside your tank to find the model number printed on the old valve. FluidmasterCross Reference Guide online to match it up. Their 400A universal and 400AH are common standard replacement valves. Measure the tank height to ensure the proper length.

Q: Why does my new fill valve still leak even when I hand tighten the coupling nut?

A: It may need an extra quarter turn with pliers to fully seal the rubber gasket inside the nut. But be very careful not to overtighten or you can crack the plastic nut or tube below it.

Q: Can I cut the new fill valve to a shorter height if it’s too tall for my toilet tank?

A: It’s not recommended to cut it shorter. Removing any of the adjustment section can prevent getting the needed water level range. Buy a shorter Fluidmaster valve to properly fit your toilet model.

Q: Do I need to use plumbers putty or a gasket when installing the new valve?

A: No, the integrated tank gasket supplied on the valve should create a good seal. You shouldn’t need any additional sealants. Just make sure the gasket sits flat and smooth in the opening.

Q: How can I quiet a noisy fill valve when the tank is refilling?

A: Try adjusting the water level lower, replacing the valve, or installing an inline water hammer arrestor. Old valves or high pressure can cause whistling and chattering.

Q: My valve float gets stuck sideways. How do I fix this?

A: Carefully bend the float arm shaft slightly so the float can hinge freely back and forth. Make sure no obstructions are blocking it from moving vertically.

Q: What should I do if the fill valve won’t shut off?

A: Make sure the float can move freely and isn’t catching. Verify the adjustment nut is tight. If not, the valve may be defective and need replacement.

Q: Why does my toilet run periodically when no one has flushed?

A: This is referred to as ghost flushing. It’s often due to a slow toilet leak or a fill valve not fully closing. Try replacing flapper, valve, or both.


Knowing how to repair or replace a fill valve is a handy DIY skill that can restore a poorly functioning toilet and prevent many flushed away gallons of water due to leaks. The Fluidmaster brand offers reliable and easy to install universal options like the 400A and 400AH valves. With a few tools and a little patience, this is a project any homeowner can tackle. Just follow each step carefully when removing your old valve and adjusting the new one. Your toilet will be back working like new again in no time!