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A running toilet is the most common plumbing fault in any house, and one of the most wasteful. It is also among the easiest to fix. Almost every case comes down to one of three things inside the tank: the flapper, the water level, or the fill valve.
How a toilet tank works
Take the lid off and set it somewhere safe, because it is heavy and it breaks. Inside you will see:
- The flapper: a rubber seal at the bottom, lifted by a chain when you press the handle
- The fill valve: the tall assembly, usually on the left, that refills the tank
- The overflow tube: an open pipe in the middle that stops the tank from overflowing
- The float: a cup or a ball that tells the fill valve when to stop
The water in the tank is clean supply water, so there is nothing unpleasant about working in it.
Test 1: is the flapper leaking?
Put a few drops of food coloring in the tank. Do not flush. Wait fifteen minutes. If color shows up in the bowl, water is getting past the flapper.
The fix:
- Close the small valve behind the toilet and flush to empty the tank.
- Check the chain first. It should have a little slack. A chain that is too short holds the flapper open, and one that is too long can get caught underneath it.
- If the chain is fine, unhook the old flapper from the two pegs on the overflow tube and take it to a hardware store to match it, or buy a universal toilet flapper.
- Wipe the rim the flapper sits on, which is often rough with mineral deposits. Fit the new one, reconnect the chain and turn the water on.
This takes ten minutes and the part costs a few dollars.
Test 2: is the water level too high?
Look at the overflow tube. If water is running over the top of it, the tank is filling too far, and the fill valve never gets to shut off.
The fix: lower the float until the water stops about an inch below the top of the tube. Most modern fill valves have a screw or a clip on the side for this. On an older ball float, turn the screw at the top of the valve, or bend the arm down very slightly.
Test 3: is the fill valve worn out?
If the flapper is sound and the level is right, but the valve hisses, never quite shuts off, or takes a very long time to fill, replace it. A toilet fill valve is inexpensive and fits nearly every toilet.
- Close the valve behind the toilet, flush, and sponge out the last of the water.
- Put a towel and a small bucket under the tank. Unscrew the supply line from the bottom of the tank, then the plastic nut that holds the fill valve.
- Lift the old valve out. Set the new one to the height given in its instructions, put it in, and tighten the nut by hand plus a quarter turn. Overtightening cracks the porcelain.
- Reconnect the supply line, clip the small refill hose to the overflow tube, turn the water on and set the level.
Allow half an hour.
The toilet that flushes by itself
If the toilet refills for a few seconds every so often with nobody near it, water is leaking slowly out of the tank. It is the flapper, nearly every time.
When to call a plumber
- Water on the floor around the base of the toilet
- The toilet rocks when you sit on it
- A crack in the tank or the bowl
- The valve behind the toilet will not close, or drips when you turn it
- You have replaced the parts and it still runs
A toilet that leaks at the base can rot the floor underneath. That is not one to leave.