How to Replace a Toilet Fill Valve

Quick answer

If the tank overfills, the fill valve won't shut off, or a new flapper didn't stop a running toilet, replace the fill valve: shut off water, drain the tank, remove the old lock nut, install a universal (or matching OEM) valve at the correct height, tighten snugly without forcing, and set water 1 inch below the overflow tube. For full diagnosis first, see why a toilet keeps running.

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

This page is the replacement how-to—not a full running-toilet diagnosis. For causes and a decision tree, use why your toilet keeps running. For the combined repair walkthrough, see how to stop a running toilet.

How to Tell if the Fill Valve Is the Problem

Adjustment fixes mis-set floats; replacement fixes worn internal seals and stuck mechanisms. Still unsure which part failed? Start at why a toilet keeps running.

What You Need Before Starting

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

Confirm the toilet shutoff behind the toilet turns before you disconnect anything.

Turn off the water supply before removing the fill valve. Do not overtighten the lock nut under the tank—porcelain cracks easily. Hand-tight plus a quarter turn with a wrench is usually enough.

Universal vs OEM Fill Valves

Most homeowners succeed with a universal adjustable kit on a standard gravity-flush toilet. Specialty toilets need the manufacturer (OEM) part.

Universal does not mean every toilet. If your tank has a branded canister, tower flush, or pressure vessel, buy the OEM valve listed for that model—or stop and ask a plumber rather than forcing a mismatch.

How to Replace a Toilet Fill Valve

1. Shut off water and drain the tank — Turn the shutoff 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.

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

4. Prepare the new valve — Set height per kit instructions—often with the valve top slightly above the overflow tube; follow the manufacturer diagram.

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

6. Attach the refill tube — Clip it so water enters the overflow tube without spraying sideways.

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

8. Test for leaks and running — Inspect the supply connection and tank bottom. Wait 15 minutes—no running sound should remain. Use a food-coloring test if flapper symptoms remain (flapper guide).

How to Adjust the Water Level

Correct water level is as important as installing the right valve. Too high = continuous overflow; too low = weak flush.

• Target: water about 1 inch below the top of the overflow tube
• Ball float: bend the arm carefully or turn the adjustment screw
• Cylinder / float cup: slide the clip or turn the dial per the valve instructions
• Water spilling into the overflow tube = level too high or valve not shutting off—lower the float first; replace if it will not hold

Always defer to the fill valve manufacturer's instructions when they differ. After any change, flush twice and listen—silence means the valve closed.

What If the Toilet Still Runs?

Do not re-diagnose the whole tank here—use the hub, then return if the valve is clearly at fault:

1. Confirm the refill tube is clipped into the overflow tube
2. Recheck water level (not spilling into the tube)
3. Confirm the flapper seals and chain slack
4. Revisit diagnosis in why your toilet keeps running and the running toilet repair guide
5. If flapper and fill valve are both new and running continues, the flush valve seat may be damaged—plumber territory

Common mistakes

• Forcing a stuck toilet shutoff instead of using the main shutoff
• Installing a universal kit on a pressure-assist or specialty toilet that needs OEM
• Overtightening the lock nut and cracking the tank
• Leaving the refill tube aimed outside the overflow tube
• Setting water level too high
• Skipping flapper inspection before blaming the fill valve alone

When to Call a Plumber

Boundaries: when to call a plumber vs DIY.

Bottom line

Toilet fill valve replacement is within reach for most homeowners who can shut off water and work inside the tank. Choose universal vs OEM correctly, tighten carefully, set the water level correctly, and verify with flush tests. Add the repair to your toilet maintenance checklist afterward.