A toilet that runs constantly, cycles on its own, or leaks is almost always a worn flapper or a bad fill valve inside the tank — both cheap, tool-light fixes. A leak at the base of the toilet is different: that usually means a failed wax ring and needs the toilet pulled and reset. Start by taking the tank lid off and watching what happens after a flush; the part that is failing usually gives itself away. A running toilet can waste hundreds of gallons a day, so this is worth fixing fast.
What you'll need
- Rubber gloves
- An adjustable wrench
- A sponge and bucket
- Towels
- Food coloring (for the dye test)
Recommended parts & supplies
- Toilet flapper — the #1 cause of a running toilet — a couple of dollars
- Toilet fill valve kit — fixes a toilet that runs or fills slowly
- Complete toilet repair kit — flapper and fill valve together for an older toilet
- Toilet wax ring — for a toilet leaking at the base
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Step by step
- 1
Run the dye test to find the leak
Take off the tank lid and put a few drops of food coloring in the tank water. Wait 15–20 minutes without flushing. If color seeps into the bowl, the flapper is leaking and letting water pass — the most common cause of a running toilet. Water on the floor around the base instead points to a wax ring or a loose connection.
- 2
Check and adjust the flapper and chain
Watch a flush: the flapper should lift, then drop and seal flat over the flush valve opening. If the chain is too short it holds the flapper open (constant running); too long and it gets trapped underneath. Adjust the chain to a slight slack. If the flapper is warped, stiff, or slimy, replace it.
- 3
Replace the flapper
Shut off the supply valve behind the toilet, flush to empty the tank, and sponge it dry. Unhook the old flapper from the pegs and chain and snap the new universal flapper in place, then reconnect the chain to the flush lever with a little slack. Turn the water back on and test. This fixes most running toilets.
- 4
Check the fill valve and water level
If the tank overfills and water runs into the overflow tube, the fill valve or float is the problem. Bend or clip the float so the water stops about an inch below the top of the overflow tube. If the valve hisses, never shuts off, or fills slowly, replace it.
- 5
Replace the fill valve if needed
With the water off and tank drained, unscrew the supply line and the locknut under the tank, lift the old fill valve out, and drop in the new one. Set its height per the instructions, reconnect the supply, turn the water on, and adjust the float. Watch for a clean shut-off with no hissing.
- 6
For a base leak, plan to reset the wax ring
If water pools at the floor with each flush, the wax ring seal has failed. This means shutting off the water, draining and removing the toilet, scraping off the old wax, setting a new wax ring, and reseating the toilet on the flange. It is doable for a confident DIYer but heavier work — if you are unsure, call a plumber before water damages the subfloor.
When to call a pro
Flapper and fill-valve swaps are squarely DIY. Call a plumber if the toilet keeps leaking at the base after a new wax ring, if the toilet rocks or the floor beneath it feels soft (a sign of subfloor water damage), or if the closet flange is cracked or below the tile and won't hold the toilet down. Also call if sewage backs up into the bowl or the toilet gurgles and drains slowly along with other fixtures — that is a main-line issue, not a tank part.
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How to Fix a Running or Leaking Toilet Yourself — FAQ
Why does my toilet keep running?
How much water does a running toilet waste?
Why is my toilet leaking at the base?
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