How to Replace a Toilet Flush Valve

Toilet handle
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Toilet Flush Valve Replacement

Toilet flush valve
Aaron Stickley

On a standard gravity-flush toilet, the flush valve is the large plastic or metal assembly that sits in the middle of the toilet tank. It is designed to control the flow of water that descends into the bowl to flush its contents into the drain system. The flush valve unit includes a long overflow tube attached to a valve seat that fits into a large opening in the bottom of the tank. The flush valve assembly also includes the flapper that seals the opening and holds water in the tank until a flush is initiated. 

The clearest sign that a flush valve needs to be replaced is when the toilet continues to run, even after the flapper and other possible causes have been addressed. The reason the toilet continues to run is that the valve seat may be worn or cracked, which prevents the flapper from making a tight seal. If a toilet flapper that is good shape doesn’t seem to seal, it's likely that a toilet flush valve needs to be replaced.

Although it's more difficult than most toilet repairs, the average handy homeowner can manage a toilet flush valve replacement. This project involves shutting off the water and disconnecting the fill valve, then removing the toilet tank from the bowl in order to remove and replace the flush valve. 

Tools and Supplies You Will Need

  • Channel-lock pliers
  • Bucket and sponge
  • Adjustable wrench
  • Large slot screwdriver
  • Hacksaw blade (if necessary)
  • Replacement flush valve
  • (2) toilet tank bolts
  • Water supply tube (if necessary)

Shut Off the Water

Begin by shutting off the water to the toilet by closing the fixture shutoff valve located near the tailpiece on the toilet's fill valve. This is normally near the bottom left side of the toilet tank. If the shutoff valve under the toilet does not shut off the water completely — or if your toilet is not equipped with a fixture shutoff valve — you can shut off the water at the main shutoff for the house. 

Flush the toilet, then remove the toilet tank lid and and use a sponge to bail out any remaining water in the bottom of the tank. Using channel-type pliers or an adjustable wrench, disconnect the water supply tube from the tailpiece on the toilet fill valve. 

Remove the Toilet Tank

Old toilet tank bolts
Aaron Stickley

The toilet tank is held in place by tank bolts, which are threaded through holes in the bottom of the tank down through the top of the bowl unit, and secured with nuts. Sometimes the nuts threaded onto the tank bolts are simple wing nuts that can be removed by hand; other times they may be traditional nuts that require a wrench or pliers. As you unscrew each nut, you may need to hold the bolt in place with a screwdriver from inside the tank to keep it from spinning in place. 

If the nuts will not come off due to corrosion, you can cut the bolt off off between the tank and the bowl, using a hacksaw blade. After the tank bolts are removed, carefully lift the tank off the bowl off and set it on a stable surface where you can work on it.  

Remove the Tank Bolts

Rusted toilet bolts
Aaron Stickley

The tank bolts may have a second set of nuts holding them onto the toilet tank. Remove these, if possible. In the case of older toilets, the insides may be so rusted that the only way to remove the bolts is to cut them off; you can accomplish this with a hacksaw or mini hacksaw.

It’s fine to cut through the rubber washer and into the bolt. Although the tank bolts can be reused if they are in good shape, it's usually better to replace them while you are replacing the flush valve. 

Remove the Old Flush Valve

Remove flush valve
Aaron Stickley

Once the tank bolts are out of the way, remove the large foam gasket covering the plastic mounting nut on the tailpiece of the flush valve. Then, use channel-lock pliers to unscrew the mounting nut. With the nut removed, pull the flush valve out of the tank. Clean up the toilet tank before installing the new hardware.

Install the New Flush Valve

Toilet flush valve
Aaron Stickley

An adjustable flush valve is a good option because it can be set to whatever height is necessary; however, most universal flush valves will work with the most toilets.

Slide the large beveled washer onto the tailpiece of the flush valve, so the beveled side of the washer faces down, then insert the flush valve through the opening in the toilet tank from the inside. Orient the flush valve unit inside the tank according to the manufacturer's directions — usually this means so the vertical overflow tube positioned near the back of the tank. 

Thread the mounting nut onto the flush valve tailpiece from the outside of the tank, and tighten it down with channel-lock pliers. As you tighten the nut, the beveled washer inside the tank should compress slightly, sealing the flush valve opening. Take care not to over-tighten the nut, as it is possible to break it. 

Place the large foam gasket over the flush valve tailpiece extending through the bottom of the tank. This gasket will serve as a "shock absorber" to cushion the tank when you set it back onto the toilet bowl. 

Install the New Tank Bolts

Toilet tank bolts
Aaron Stickley

Thread the tank bolts through holes in the bottom of the toilet tank, with one rubber washer under the head of each bolt, and another rubber washer and a metal washer threaded over the bolts from the outside of the tank. The goal is for the porcelain to be sandwiched by rubber washers. Thread a mounting nut onto each bolt and tighten it just enough to slightly compress the rubber washers. 

Set the Tank Onto the Bowl

Replacement toilet tank bolts
Aaron Stickley

Carefully set the tank onto the toilet bowl so the tank bolts slide down through the holes in the top of the bowl. Thread metal washers and nuts onto the bolts and tighten them down by hand. Standard nuts should be tightened slightly further with a wrench, but take care not to crack the porcelain. If you aren't sure how tight to go, let the tank fill with water and let the weight help push the tank down; then you can tighten the nuts.

Connect the Water Supply

Toilet water supply
Aaron Stickley

Reattach the water supply tube to the tailpiece on the toilet's fill valve (you may want to replace the water supply tube with a new one at this time). Turn on the water to the toilet. Connect the flapper chain to the toilet handle rod from inside the tank.

Make any required adjustments to the flush valve height so that the water level is at the recommended line and the overflow tube is about 1 inch above that. Most importantly, check for leaks by flushing the toilet several times.