The fill valve is the tall assembly on the left side of the tank that refills it after a flush. When it fails, symptoms include continuous running, a tank that refills painfully slowly, a whistling or hammering noise, or a water level that will not settle where you set it.
Replacement is one of the more approachable plumbing jobs. Modern universal fill valves fit almost every domestic toilet and cost very little.
What You Need
- A universal fill valve
- An adjustable wrench or slip-joint pliers
- A sponge and a towel
- A shallow bowl or tray
Buy the valve before starting, and take a photo of your existing setup to compare. If the supply line is more than about ten years old, or is plain plastic rather than braided steel, replace it at the same time — it is inexpensive and it is the component most likely to fail catastrophically.
Step 1: Shut Off and Drain
Close the shut-off valve on the wall behind the toilet, turning clockwise. If there is no shut-off valve, or it will not close, shut off the water to the house.
Flush and hold the handle down to empty as much water as possible. Sponge out what remains in the bottom of the tank and dry it. Getting the tank genuinely empty makes the rest of the job far less messy.
Step 2: Disconnect the Supply Line
Put the tray under the connection — there will be water in the line regardless of how well you drained the tank. Unscrew the supply line from the bottom of the fill valve shank. Hand-tight is often enough; use the wrench gently if not.
Step 3: Remove the Old Valve
Under the tank, unscrew the large plastic locknut holding the fill valve shank through the tank floor. It is usually hand-loosenable; if it is seized, grip it with slip-joint pliers and turn carefully. Do not lever against the ceramic.
Once the nut is off, lift the old valve out of the tank, unclipping the small refill tube from the overflow pipe as you go.
Step 4: Set the Height
This is the step people skip, and it matters. Most universal valves telescope to adjust height. The critical rule: the top of the valve must sit at least an inch above the top of the overflow tube. That gap is what stops tank water being siphoned back into the household supply.
Adjust the valve to height before fitting it — usually by twisting the body to unlock, extending it, and twisting to lock.
Step 5: Fit the New Valve
Drop the valve through the hole in the tank floor with its rubber washer seated on the inside. From underneath, thread the locknut on and tighten by hand, then no more than about a quarter turn with the wrench.
Overtightening here cracks tanks. The seal comes from the washer, not from force.
Step 6: Connect the Refill Tube
Clip the small flexible tube from the valve onto the overflow pipe, using the angle adapter supplied. It must discharge into the overflow tube, not below the waterline — a tube pushed down inside the tube can siphon water continuously.
Step 7: Reconnect and Test
Reattach the supply line, hand-tight plus a gentle nudge. Open the shut-off valve slowly and watch the connections while the tank fills.
Set the water level about an inch below the top of the overflow tube, using the adjustment on the valve. Flush several times and check for drips at the locknut and the supply connection. Leave a dry sheet of kitchen paper under both for an hour, then check it.
If It Still Runs Afterwards
Then the fill valve was not the fault. Work back through the checks in why your toilet runs constantly — a worn flapper is the more common cause, and it is even cheaper to fix.
If the problem is a tank that refills too slowly rather than one that never stops, see why your toilet is not filling up with water, which covers supply-side restrictions as well as the valve.
For the other components in the same tank, our toilet hardware repair guide covers flappers, flush valves and handles.
