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How to Repair Toilet Flush Valves

Chris Deziel
Table of Contents

When your toilet runs or doesn't flush properly, fix it by replacing the flapper or canister seal, adjusting the chain or replacing the flush valve.

The flush valve on a toilet is the mechanism that fits over the siphon hole in the tank and prevents water from draining out until you activate it by pushing the flush handle. In most toilets, the working part of the valve is a rubber flapper, but don't be surprised if you open your toilet tank and find a sealed canister instead -- that's the type your toilet has if you have a dual-flush control, and they are becoming common on single-flush toilets, too. Don't be dismayed if you find one, since they are just as easy to repair as flapper valves.

Troubleshooting a Flush Valve

The principle of operation of a flush valve is uncomplicated, and diagnosing problems is usually straightforward.

  • Running Toilet: The most common symptom of a flush valve malfunction is a running toilet -- one that fills continuously or cycles on and off when you aren't using it. This is caused by a poor seal, which may be the fault of a worn flapper or canister gasket or that of mineral deposits collecting on the valve outlet. 
  • Flush Lever Doesn't Work: If you push the flush lever or button and nothing happens, the problem is usually related to the chain or -- on some canister valves -- the rod that connects the valve to the flush button. More often than not, the chain has become disconnected and needs to be reattached.
  • Toilet Won't Stop Flushing: If your toilet has a flapper, this is another chain-related problem; the chain is too short. If your toilet has a canister, the valve inside the canister is sticking in the open position.
  • Incomplete Toilet Flush: As far as flapper valves are concerned, incomplete flushes are also usually related to the chain; in this case, the chain is too long, and the flapper isn't lifting high enough for water pressure to keep it up. This isn't a common problem with canister valves.

Repairing a Flapper Valve

Replacement Procedure

  1. Turn off the water supply valve and flush the toilet to drain the tank.

  2. Disconnect the chain from the flush handle by lifting the hook. Remove the flapper either by pulling the ears off the posts on the overflow tube or lifting it up and off the tube.

  3. Scrape or sand off any mineral deposits you see on the valve opening that could be preventing the flapper from seating properly

  4. Take the flapper to the hardware store to find a suitable replacement. Many toilets accept a universal flapper, but some require a specific type.

  5. Replace the flapper by reversing the procedure for removing it. Reconnect the chain to the flush handle, making it long enough to lift the flapper between 45 and 60 degrees when you push the handle. Tun on the water and do a test flush, then adjust the chain length, if necessary.

Rubber and plastic flappers are inexpensive, and if yours isn't making a proper seal, the best course of action is to replace it. If you aren't sure if the flapper is actually leaking, put some food coloring in the tank and leave the toilet overnight without using it. Colored water in the bowl in the morning confirms a leak.

Replacing the Gasket on a Canister

The procedure for replacing a canister gasket is simple. Drain the tank, unhook the chain -- if there is one -- rotate the canister 90 degrees and lift it out of the tank. Turn it over, pull off the old gasket, fit on a new one and replace the canister.

Replacing the Flush Valve

If the flush valve is old and encrusted with minerals, the best course may be to replace it. Although this is easy to do, it requires removal of the tank. Once you have the tank separated from the bowl, simply unscrew the lock nut holding the valve to the tank, using adjustable pliers, and lift out the valve and secure the new one with the lock nut that comes with it. If you prefer, you can replace a flapper valve with a canister-style one, and vice versa.


Replace the bolts holding the tank to the bowl as well as the sponge gasket on which the tank rests when you replace the flush valve.