How do I replace a toilet shut-off valve?

Replace it when it leaks, won't turn, or won't shut the water off fully. BrassCraft, a maker of water stops, is direct about it: "Do not reuse, inspect annually, replace if damaged, deterioration or corrosion is detected." Signs to look for are corrosion on the valve, drips at the handle or at either nut, and a handle that will not move.

You also need a valve if the toilet does not have one. The 2024 International Plumbing Code says shutoff valves shall be installed "on the fixture supply to each plumbing fixture" with exceptions that include bathtubs and showers in one- and two-family homes. The code adds that "access shall be provided to all full-open valves and shutoff valves." Kohler's installation guide for a toilet says the same in practical terms: if the existing toilet does not have a supply shut-off valve below the tank, install one before installing the new toilet.

A working valve does more than let you stop a leak. It lets you work on the toilet without shutting off the whole house. Our guide on how to shut off the water to just one fixture shows how these valves work.

One more use for it: keep it fully open during normal use. Kohler's troubleshooting chart for a toilet that will not refill starts with "Fully open the water supply shut-off valve." BrassCraft's instructions also say "stop must be used in the fully opened or fully closed position," so do not leave it half open to slow the fill.

Pick the valve by the pipe it connects to, not by the toilet. BrassCraft's instructions say its stops come in "a variety of configurations," so you must "select the inlet and outlet instructions that apply to the product purchased." The inlet is the side that connects to the wall pipe. The instructions cover these inlet types:

• Copper compression. A nut and sleeve squeeze onto the copper pipe. BrassCraft says this is for type L or M copper only.
• Threaded (female iron pipe). The valve threads onto a pipe nipple with thread sealant.
• Sweat, or soldered. The valve is soldered onto the copper stub.
• CPVC. The valve is glued to CPVC pipe with solvent cement.
• PEX. The valve connects with a crimp, compression or expansion fitting and the right tool.
• Push connect. The pipe pushes into the valve.

Quarter-turn stops close with a 90 degree turn of the handle. BrassCraft's instructions also cover multi-turn stops, which work like a small faucet handle. Either kind can serve a toilet.

The outlet is the side that goes to the supply line. The 2024 plumbing code lists minimum fixture supply pipe sizes for toilets: 3/8 inch for a flush-tank water closet and 1/2 inch for a one-piece water closet. Check the size on your old valve, or take it with you to match it.

1. 1Turn off the water. BrassCraft says "be sure to shut off water before starting," for every type of connection. If the valve you are replacing is the only shutoff for that toilet, close a valve upstream, usually the main. Flush the toilet and hold the handle down to empty the tank. Sponge out what is left.
2. 2Disconnect the supply line. Fluidmaster's steps are to turn off the supply at the shutoff valve, then remove the old supply connector and clean all connector threads. Have a bucket or towel ready, because water will run out of the line.
3. 3Remove the old valve. How it comes off depends on how it was attached. A threaded valve unscrews. A soldered or glued one has to be cut off the pipe.
4. 4Prepare the pipe. BrassCraft says to "be sure stub out and riser are square, round and free of burrs." BrassCraft warns that if the stop is not square to the tube, "this could affect the ability to get a good connection."
5. 5Install the new valve for your pipe type.

• Copper compression. Slide the nut and sleeve onto the tube. BrassCraft says a drop of general purpose oil makes tightening easier, and that you should not use putty, gasket material or thread seal tape. Hand tighten the nut as far as it will go, then use hand tools to tighten 3/4 turn more. Keep the valve seated and square to the tube. BrassCraft's warning: "DO NOT OVERTIGHTEN as this could lead to future failure."
• Threaded. Apply thread sealant to the pipe nipple, thread the valve on and wrench tighten it. Make sure the outlet faces the right way.
• Sweat. For quarter-turn stops, BrassCraft says to make sure the stop is open while you solder, not to turn it off until it has fully cooled, and not to use a wet rag to cool it. This takes flux, solder and a torch.
• CPVC. Use only CPVC cement or an all-purpose cement that meets ASTM F-493, or the joint may fail. BrassCraft warns that too much cement can clog the waterways.

1. 1Flush out debris before you connect the toilet. Kohler says to turn on the water and "allow water to flow through the supply pipe to flush the system of any debris before connecting fill valve." Point the valve outlet into a bucket, open it briefly, then shut it.
2. 2Reconnect the supply line. Fluidmaster says you only need an adjustable wrench to snug the metal nut that connects to the shut-off valve. Its instructions add "do not over tighten shut off valve." Our guide on how to replace a toilet supply line covers the other end of the line.
3. 3Open the water slowly and check for leaks. Fluidmaster says to check carefully at the shutoff valve and that if a leak appears, "tighten nut just enough to provide a leak-free joint." BrassCraft's steps for a slip-joint outlet say that if the nut leaks, turn off the water, back the nut off completely, realign it and retighten. Do not just keep cranking a leaking nut.

Check again after an hour, and again the next day. A slow drip behind a toilet can go unseen for a long time and damage the wall or floor.

Some versions of this job are easy and some are not. Call a plumber if:

• The pipe is copper and the stop needs to be soldered. It takes a torch, and heat can harm a valve's inner parts. BrassCraft's instructions include special steps to protect them.
• The old valve is stuck or the pipe behind it moves. Forcing it can damage the pipe behind it.
• You cannot shut the water off. If the main or the upstream valve will not close fully, you cannot safely take the old valve off.
• The pipe is corroded, crooked or damaged. A new valve can only be as good as the pipe it seals on.
• A new valve keeps dripping. A leak that returns after you retighten needs a new joint, not another turn of the nut.
• The valve is behind a wall or in a spot you cannot reach. BrassCraft says its stops are "for use with water in accessible locations only," and the code says the same about access.

HQ Plumbing and Air replaces toilet shut-off valves and supply lines, and we can do it while we are there for anything else. We are licensed and insured, we give free estimates, and you get the price up front. If your toilet is old enough that you are wondering about the whole fixture, see how to know when to replace a toilet.

If the stop only drips at the handle, it may just need its packing nut snugged a little. See why a shut-off valve leaks at the handle before you replace it.

With a new stop in place, adding a bidet seat is a short job. See how to install a bidet attachment.