Running toilet? How to find the cause and stop it

Why it matters

The EPA calls a worn flapper a common culprit that can make a toilet flush on its own or leak silently, wasting thousands of gallons a year. Denver Water, citing EPA figures, puts an average leaking toilet at about 200 gallons a day. Toilets are also the largest indoor water user in a typical home, at nearly 30 percent of indoor use, according to EPA WaterSense.

1. Do the dye test

Put a few drops of food coloring in the tank and do not flush. EPA WaterSense says that if color shows up in the bowl within 10 minutes, the toilet is leaking. Flush afterward so the dye does not stain.

2. Check the flapper

The flapper is the rubber seal at the bottom of the tank. Denver Water names worn-out flappers as the biggest cause of toilet leaks. If the tank refills by itself every so often, Fluidmaster’s instructions say the tank is losing water and the flapper and its seat should be cleaned. A flapper that is warped, stiff or slimy usually needs replacing; take the old one to the store so the new one matches.

3. Check the chain

The chain connects the flush handle to the flapper. Too tight, and the flapper cannot seal; too loose, and it can get caught under the flapper. Fluidmaster recommends about half an inch of slack.

4. Check the water level

Water should stop below the top of the overflow tube – Fluidmaster suggests about half an inch below. If water spills into the tube, the fill valve or float is set too high. Denver Water says a float that is not set properly is another common cause of leaks, and a toilet leaking down its overflow tube can waste 100 to 250 gallons a day. Most fill valves have an adjustment screw or clip for the float.

5. A hissing or noisy fill valve

If the fill valve hisses or never fully shuts off even with the level set right, the valve itself may be worn. Replacing a fill valve is a common repair, but it means shutting off the water and disconnecting the supply line. If the shut-off valve behind the toilet is stuck or leaks when you turn it, stop and call a plumber – forcing old valves can break them.

Repair or replace the toilet?

Tank parts are inexpensive and most running toilets only need a flapper or fill valve. Replacing the whole toilet makes sense when the bowl or tank is cracked or the toilet is old and uses a lot of water. Federal rules cap new toilets at 1.6 gallons per flush, and WaterSense-labeled toilets use 20 percent less; older toilets can use as much as 6 gallons per flush, according to EPA WaterSense.

When to call a plumber

• Water is leaking onto the floor around the base – often a failed wax ring.
• The tank or bowl is cracked.
• The shut-off valve will not close, or it leaks.
• You have replaced the flapper and fill valve and it still runs.
• The toilet overflows, or other drains gurgle or back up when you flush – that can point to a clog further down the line.