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How do you replace a toilet fill valve?

Updated August 2026

20–30 minutes · Easy DIY

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Shut the supply, empty the tank, unscrew the old valve from underneath, and drop in a $12 to $25 universal fill valve. Twenty to 30 minutes, one pair of pliers. This is the repair when a toilet hisses between flushes, refills on its own with a dry bowl, or keeps running after a new flapper has already cleared that suspect. Universal valves fit nearly every two-piece toilet built in the last 40 years and telescope to match tank height, so a brand-specific part is rarely necessary.

What you need

Before you start: Every part of a toilet tank is either brittle plastic or porcelain, and both punish enthusiasm. Hand-tighten the lock nut and the supply coupling: a wrench on either one splits the nut or, worse, the tank, and a cracked tank means a new toilet. Close the supply stop before you start and open it slowly at the end while watching the connections fill. If the stop will not close or begins dripping once you turn it, shut the main and replace the stop before you finish. Swap a braided supply line older than 8 years while you are down there, since a $10 line prevents a four-figure water damage bill.

Steps

  1. Close the supply stop on the wall behind the toilet, then hold the flush lever down until the tank drains as far as gravity takes it.
  2. Sponge the last inch of water out of the tank into the bucket. A dry tank is the difference between a clean job and a soaked cabinet floor.
  3. Put the towel and a shallow pan under the supply connection, then unscrew the supply line coupling nut from the bottom of the valve shank, by hand or with pliers.
  4. Unscrew the plastic lock nut above the coupling and lift the old valve out of the tank, unclipping its small refill tube from the overflow on the way.
  5. Set the height of the new valve before it goes in. Most twist and telescope; adjust so the critical level mark on the body sits at least 1 inch above the top of the overflow tube.
  6. Drop the valve through the hole with its shank washer inside the tank, hold it upright, and hand-tighten the lock nut from below. A quarter turn with pliers is the absolute maximum after hand tight.
  7. Reconnect the supply line hand tight plus a quarter turn, then clip the refill tube to the overflow with the little angle adapter. That tube must stay above the water line, never pushed down inside the overflow, or it siphons continuously.
  8. Open the stop slowly and let the tank fill. Set the shutoff level about 1 inch below the top of the overflow tube with the thumbscrew or clip, flush three times, and check the shank and coupling with a dry paper towel after 10 minutes.

Or hire it out

A plumber charges $125 to $250 for a fill valve replacement, and the minimum service charge is most of it. The part is $12 to $25 and the actual labor is about 20 minutes.

Done. Now the part everyone skips: doing it again on schedule. Log it in OnOtto and the next reminder for fill valve swaps sets itself.

Log this task, get the next reminder

Frequently asked questions

Flapper or fill valve: which one is failing?

Listen and then dye. A hiss or a brief refill every few minutes with no visible movement in the bowl points at the fill valve. Color in the bowl 15 minutes after you tint the tank points at the flapper, since that proves tank water is escaping past the seal. Do the dye test first because a $6 flapper is the cheaper thing to be wrong about. The full sequence is on how to fix a running toilet.

Do I need a brand-specific fill valve?

Rarely. One universal valve covers the overwhelming majority of standard two-piece toilets and adjusts through a range of roughly 9 to 14 inches of tank height. Two exceptions: very low-profile or one-piece toilets need the short-body version, so measure from the tank bottom to the rim before you buy, and pressure-assist toilets use an entirely different cartridge that is sold by model. Check the label inside the tank lid if you are unsure which you have.

The water level keeps creeping up after the swap.

Two likely causes. The float is set too high, which is a thumbscrew or clip adjustment on the shaft; drop it until the water stops an inch below the overflow. Or debris knocked loose during the swap is holding the new seal open. Fix that by closing the supply, twisting the cap off the top of the valve, holding an upside-down cup over the opening, and opening the supply for 15 seconds to blow the line clear. Then verify with the dye test on how often to check a toilet for leaks.

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