On a standard gravity-flush toilet, the flush valve is the large plastic or metal assembly that sits inside the toilet tank near the middle. 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, which 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 water 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 in good shape doesn’t seem to seal, it's likely that a toilet flush valve itself is cracked or worn and 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.
Replacing a toilet flush valve is not a difficult job, but it requires some patience. It requires that you remove the toilet tank from its position on the bowl, and the porcelain tank can easily crack if you're not careful as you work.
Make sure to buy a flush valve that fits your toilet. You may want to take the old flush valve to the hardware store for comparison to ensure you buy the proper size. The hardware store clerk can advise you on the best flush valve for your toilet.
Since you will have the tank detached anyway, this might be a good time to consider a full toilet tuneup by replacing the water fill valve (ballcock) and water supply tube at the same time you are replacing the flush valve.
Equipment / Tools
- Channel-lock pliers
- Bucket and sponge
- Adjustable wrench
- Large standard 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 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
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.
Remove the nuts threaded onto the tank bolts in the bottom of the tank. 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 between the tank and the bowl, using a hacksaw blade.
Remove the Tank Bolts
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 nuts and 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.
After the tank bolts are removed, carefully lift the tank off the bowl and set it on a stable surface where you can work on it.
Cutting the tank bolts off can be challenging; you may need to hold the hacksaw blade itself, without the handle, to get the right angle. If this is necessary, work with caution and wear protective gear.
Remove the Old Flush Valve
Once the tank bolts are out of the way and the tank is on a steady work surface, remove the large foam gasket covering the plastic mounting nut on the tailpiece of the flush valve.
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
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 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 the vertical overflow tube should be 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
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
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. Apply a small amount of weight evenly to the top of the tank to compress the washers slightly as you tighten the nuts. Make sure the tank is level from side to side.
Connect the Water Supply
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 one inch above that. Most importantly, check for leaks by flushing the toilet several times. Tighten any connections that are leaking.
When to Call a Professional
For a professional with the right tools, flush valve replacement is a fairly quick, inexpensive job. If the idea of detaching the toilet tank makes you a little nervous—or if the toilet is very old with bolts and nuts that are badly corroded—you may want to call in a plumber to do the job. The labor costs should be a minimal house-call charge.