How to Replace a Toilet Fill Valve

Take the lid off the tank and watch it fill. A failing fill valve does not shut off cleanly. It drops to a thin trickle and keeps running, and the water climbs above the float instead of stopping. A whistle or a screech while the tank fills is the other giveaway. If that is what you are seeing, the valve is the part to replace.

Find the supply valve on the wall behind the toilet and turn it clockwise until it stops. Give the handle a flush afterwards to confirm nothing refills. If the shutoff is seized or keeps weeping, close the main instead rather than forcing it.

Hold the handle down so as much water as possible drains out, then get the rest with a sponge and wring it into a container. Flushing never empties a tank completely and there is always an inch or so sitting in the bottom. Get it as dry as you can before you go near the supply line.

Loosen the nut where the supply line meets the bottom of the tank. Working the connector loose a little first gives you room to turn it. Keep a bucket or a towel underneath, because water is still sitting in that line and it will run out.

Undo the large plastic lock nut on the underside of the tank. Whatever water is left drains as it comes free, so keep the bucket in place. Then lift the old fill valve straight up and out.

The top of the valve needs to sit about three inches above the overflow pipe. Lay the old and new valves side by side, measure the old one, and twist the base of the new one to lengthen or shorten it until they match. On this toilet that came out at ten and three quarter inches.

Push the refill tube onto the refill port on the side of the valve. On a standard toilet you then clip the other end over the rim of the overflow pipe with the little plastic clip that came in the bag.

Drop the valve down through the hole in the bottom of the tank and hold it upright. This tank has a collar-style flush valve, so the refill hose feeds into its own port rather than clipping to a pipe. Check the height against the overflow one more time before you tighten anything.

Thread the lock nut on from underneath and snug it by hand, then reconnect the supply line to the valve shank. Plumbers tape on these threads is optional and rarely needed, since the seal comes from the rubber washer rather than the threads. Tighten both by hand.

Open the supply valve slowly and let the tank fill. Run your hand around both connections, underneath and inside, and look for damp. A slow weep is easier to catch now than after you have put the lid back on.

The water should stop about half an inch below the top of the overflow pipe. If it sits too high or too low, turn the adjustment knob on top of the valve to move it. Then flush once more and confirm the tank refills to the right level, shuts off cleanly, and stays dry.