How to Replace a Toilet Flush Valve: Flapper and Dual Flush Types

If coloured water from a dye test appears in the bowl, or your tank refills by itself every so often, water is escaping through the flush valve. Before you replace the whole valve, it helps to know that the fix is often smaller: a new flapper, a new canister seal, or a cleaned seat. This guide explains how to decide, and how to do each repair.

Know your flush valve type

1. Flapper flush valve (lever toilets) A rubber flapper sits on a round seat at the bottom of the tank and is lifted by a chain from the handle. It is common in North America and much of Latin America. The opening size is often 2” or 3”. Check the old part, because the flapper must match the seat diameter.

2. Canister / tower flush valve (push-button toilets) A vertical valve body lifts straight up when you press the button. A ring-shaped rubber seal at the base closes against the seat. It is common in Europe, and on many dual flush toilets worldwide. Many can be removed from their base with a twist, without taking the tank off.

3. Siphon (UK) Older UK cisterns often use a siphon instead of a valve. Siphons rarely leak into the bowl the same way. A failing siphon usually means the toilet needs several pumps of the handle to flush. Siphon repair isn’t covered in this guide.

Small fix or full replacement?

What you see	Usually enough	Full valve needed when
Flapper soft, warped, leaves black marks	New flapper	Seat is cracked or badly pitted
Canister seal flattened or cracked	New seal	Valve body broken, clips snapped
Leak only after flushing	Chain/button adjustment	Overflow pipe cracked
Leak between tank and bowl (onto the floor)	—	Tank-to-bowl gasket and/or full valve; tank must come off

Safety notes

• Turn off the water at the shut-off valve behind the toilet and flush to empty the tank.
• Put a towel down. Wear gloves if the tank has chemical tablet residue.
• If the job requires removing the tank from the bowl, get help. Ceramic tanks are heavy and can crack if dropped or if bolts are over-tightened.

Repair A: Replace a flapper

1. Turn off the water and flush to drain the tank.
2. Unhook the chain from the handle lever.
3. Slide the flapper ears off the pegs on the sides of the overflow pipe, or unclip the ring if it is a ring-mounted type.
4. Clean the seat with a soft non-scratch pad. Feel for rough spots or cracks.
5. Fit the new flapper the same way the old one was fitted.
6. Reattach the chain. With the flapper closed, there should be a small amount of slack, usually about one or two links. Too tight keeps it open, too loose can catch underneath it.
7. Turn on the water, let the tank fill, and flush several times. Repeat the dye test.

Some flappers are adjustable to control how long they stay open. If you have a low-flow toilet, follow the toilet maker’s recommendation for the setting.

Repair B: Replace a canister/tower seal (push-button cisterns)

1. Turn off the water and press the button to empty the cistern. Sponge out the remainder.
2. Remove the lid. On push-button toilets, the button is often part of the lid or has to be unscrewed first. Check your model.
3. Disconnect any cables or rods from the button to the valve if necessary.
4. Release the valve body from its base. Many designs turn anticlockwise to unlock, and others use clips. Press down gently while turning so that you don’t break the locating tabs.
5. Lift the valve out and remove the seal from the bottom.
6. Clean the seat in the base. Don’t use sealants or grease on the seat unless the manufacturer specifically says to, because some products damage rubber seals.
7. Fit the new seal fully into its groove.
8. Refit the valve, lock it into its base, reconnect the button linkage and test both full and half flush.

Repair C: Replace the complete flush valve

Replacing the complete valve (including the part bolted through the tank) usually means taking the tank off a close-coupled toilet.

1. Turn off the water, drain the tank and sponge it dry.
2. Disconnect the supply hose from the fill valve.
3. Undo the tank-to-bowl bolts. Hold the bolt heads inside the tank while you unscrew the nuts underneath.
4. Lift the tank off and lay it on a towel, upside down or on its back.
5. Remove the large flush valve lock nut and the old tank-to-bowl gasket, then remove the valve.
6. Clean the tank opening.
7. Fit the new valve with its sealing washer inside the tank and tighten the lock nut snugly. Overflow height must sit below the fill valve’s critical level, so trim it only if the instructions allow.
8. Fit a new tank-to-bowl gasket and new bolt washers.
9. Set the tank back on the bowl and tighten the bolts evenly and alternately, a little at a time, until the tank is firm. Don’t over-tighten, because ceramic can crack.
10. Reconnect the supply, turn on the water and check every joint for drips before you put the lid back.

Matching parts across markets

Flush valve sizes and connections differ between regions and brands. A North American 2” flapper won’t fit a European push-button tower valve, and many European cisterns use brand-specific valves. Before buying, measure the seat diameter, note the brand and model on the cistern (often inside the lid or on the back), and compare with the part’s specifications. Our article on European vs American toilet tank parts explains the main differences.

Frequently asked questions

How do I know if it’s the flapper or the fill valve? If the water level is below the overflow pipe but the tank keeps refilling, it’s the flush side. If water runs into the overflow pipe, it’s the fill side. See our running toilet diagnosis guide.

Can I convert a lever toilet to dual flush? Conversion kits exist for some toilets, but fit depends on the seat size and tank design. Check compatibility carefully.

Why does my new flapper still leak? The seat may be scaled or damaged, the chain may be too tight, or the flapper may be the wrong size or type for the toilet.

Does a half-flush button use a separate seal? Usually no. Most dual flush canisters use one seal, and the button controls how far the valve lifts or how long it stays open.

How often should seals be replaced? It depends on water quality and cleaning products. Inspect them whenever you notice a leak.

For distributors

Flush valves, flappers and dual flush canisters are steady sellers for plumbing merchants and DIY retailers. If you distribute sanitary spare parts in Europe or Latin America, visit our For Distributors page to ask about our flush valve range, seal sizes and repair kits, including private-label packaging. Please tell us which standards your market requires. Certification status must be confirmed for each product before ordering.