How to Replace a Toilet Fill Valve

Quick answer

If the tank overfills, the valve won't shut off, or a new flapper didn't fix a running toilet, replace the fill valve: shut off water, drain the tank, remove the old valve's lock nut, install a universal valve at the correct height, tighten snugly without forcing, and set the water level 1 inch below the overflow tube.

The fill valve controls how water refills the tank after each flush. When it sticks open, runs loudly, or can't hold the correct water level, the toilet may run continuously or spill water into the overflow tube. If you've already ruled out a worn flapper, the fill valve is the next logical repair.

This guide focuses on fill valve replacement. For diagnosis of running causes, see why your toilet keeps running. For the combined repair walkthrough, see how to stop a running toilet.

When to replace vs adjust

Adjustment fixes mis-set floats; replacement fixes worn internal seals and stuck mechanisms.

Tools needed

• Adjustable wrench or channel-lock pliers
• Bucket and towels
• Flashlight
• Scissors or utility knife (for shank trim if needed)

Materials needed

• Universal fill valve kit ($10–$20)
• Clean rag
• Optional: Teflon tape if kit instructions specify

Step-by-step replacement

1. Shut off water and drain the tank — Turn the shutoff valve behind the toilet clockwise. Flush and hold the handle to empty as much water as possible. Sponge out the rest.

2. Disconnect the supply line — Place a bucket under the connection. Unscrew the supply line from the bottom of the fill valve shank (where it passes through the tank bottom).

3. Remove the old fill valve — Unclip the refill tube from the overflow tube. Loosen the lock nut under the tank that holds the valve shank. Lift the old valve out.

4. Prepare the new valve — Universal kits include an adjustable height column. Set height per kit instructions—typically 1 inch above the overflow tube top is a common starting point; follow the manufacturer diagram for your kit.

5. Install the new valve — Insert the shank through the tank hole. Hand-tighten the lock nut under the tank, then snug with a wrench—do not overtighten. Reconnect the supply line.

6. Attach the refill tube — Clip the small refill tube to the overflow tube so it directs water into the tube without spraying sideways.

7. Turn water on and set the level — Open the shutoff slowly. Adjust the float or adjustment screw until water stops about 1 inch below the overflow tube rim. For adjustment-only fixes without replacement, see how to adjust toilet water level. Flush twice and recheck.

8. Test for leaks and running — Inspect the supply connection and tank bottom for drips. Wait 15 minutes—no running sound should remain. Run a food-coloring test if you previously had flapper-related symptoms (see flapper replacement guide).

Height adjustment reference

Always defer to the fill valve manufacturer's instructions when they differ from general rules.

Common mistakes

• Overtightening the lock nut and cracking the tank
• Leaving the refill tube aimed outside the overflow tube (causes splash and noise)
• Setting water level too high (constant overflow into tube)
• Skipping flapper inspection—always confirm the flapper seals before assuming the fill valve is the only issue

When to call a plumber

Bottom line

Fill valve replacement is still within reach for most homeowners comfortable shutting off water and working inside the tank. Match part height, tighten carefully, set the water level correctly, and verify with flush tests. Add the repair to your toilet maintenance checklist routine afterward.