⏱ 20 to 60 minutes
💰 Save $150 to $300
How to Fix a Running Toilet — Complete Guide 2025
A running toilet wastes up to 200 gallons of water per day and adds $70 or more to your monthly water bill. This guide diagnoses the exact cause and walks you through every fix — flapper, fill valve, flush valve, and float — with parts costing under $20.
A running toilet is one of the most common — and most wasteful — home plumbing problems. The good news is that 95% of all running toilet issues are caused by one of just three inexpensive parts inside the toilet tank, and replacing any of them takes less than an hour with no special tools. You do not need to turn off the water to the whole house, you do not need to disassemble the toilet, and you definitely do not need to call a plumber.
Step 1 — Diagnose Your Running Toilet
Before buying any parts, identify exactly what is causing the problem. Remove the tank lid and observe what is happening inside while the toilet is running. Select the symptom that matches what you see:
The Three Parts That Cause 95% of Running Toilets
Every toilet tank has the same basic components. Understanding what each part does helps you buy exactly the right replacement and fix the problem on the first attempt:
Most common cause
Second most common
Often free to fix
Less common
How Much Is Your Running Toilet Costing You?
A running toilet is not just annoying — it is silently adding significant cost to your monthly water bill. Here is exactly how much different levels of running waste:
A constantly running toilet wastes up to 73,000 gallons per year — enough to fill an average swimming pool. At average US water rates of $0.004 per gallon, that is nearly $300 wasted annually from one toilet. A $10 flapper replacement pays for itself within hours of installation.
Step-by-Step Fix — Flapper Replacement
The flapper is the cause of running toilets in approximately 70% of all cases. Start here. This repair takes under 20 minutes and costs $5 to $15:
Turn Off the Water Supply to the Toilet
Look behind the toilet at the base of the wall — there is a small oval or teardrop-shaped shutoff valve on the water supply line. Turn it clockwise all the way until it stops. This stops water from entering the tank. Unlike faucet repairs, you do not need to shut off water to the whole house — just this one valve.
💡 If the valve is stiff or stuck, use pliers with a cloth — do not force it
Flush the Toilet and Empty the Tank
Flush the toilet once after turning off the supply valve. The tank will empty and will not refill because the water supply is now off. This gives you a dry tank to work in. If a small amount of water remains in the bottom of the tank, this is normal — soak it up with a sponge or old towel.
Remove the Old Flapper
The flapper is the rubber disc at the very bottom of the tank attached to the flush valve seat. It connects to the toilet via two side ears that hook onto pegs on the overflow tube — simply unhook both ears by pushing them inward and lifting. The flapper is also connected to the flush handle via a small chain — disconnect the chain from the flapper by unhooking the clip or loop at the flapper end.
Bring the old flapper to the hardware store to match the exact size and model. Toilet flappers are not universal — the wrong size will not seal correctly.
📸 Photograph the flapper and chain connection before removing
Install the New Flapper
Attach the new flapper’s ear loops onto the pegs on the overflow tube — press each ear down and outward until it snaps into place. Reconnect the chain from the flush handle to the new flapper. The chain should have about half an inch of slack — enough to allow the flapper to open fully when you flush but not so much slack that it gets caught under the flapper when it closes.
🔧 Adjust chain length so flapper seals completely after each flush
Turn Water Back On and Test
Turn the supply valve back on counterclockwise. Allow the tank to fill completely — this takes about 60 to 90 seconds. Once full, listen carefully for any hissing or running sounds. Flush the toilet and watch the flapper seal completely after the flush cycle finishes. Add a few drops of food coloring to the tank water and wait 15 minutes without flushing — if color appears in the bowl, the flapper is still not sealing and needs to be repositioned or replaced with a different size.
✅ The food coloring test is the most reliable way to confirm a complete seal
How to Adjust or Replace the Fill Valve and Float
If replacing the flapper did not fix the running, or if water is overflowing into the overflow tube, the fill valve or float adjustment is your next step:
| Problem | Fix | Cost | Time |
|---|---|---|---|
| Water level too high — reaching overflow tube | Adjust the float down — pinch the adjustment clip on the fill valve and slide the float cup down the valve stem about 1 inch | Free | 2 minutes |
| Fill valve hisses constantly after tank fills | Replace the fill valve completely — Fluidmaster 400A is the universal standard replacement ($10 to $14) | $10 – $14 | 20 – 30 min |
| Tank takes more than 3 minutes to fill | Check the supply valve is fully open; if so, replace fill valve | $10 – $14 | 20 – 30 min |
| Ghost flushing every few minutes | Flapper leak — do the food coloring test and replace flapper if color appears in bowl | $5 – $15 | 15 – 20 min |
| New flapper still leaks — water colored test positive | Flush valve seat is pitted — replace seat or install a Korky flush valve seal kit | $15 – $35 | 30 – 45 min |
The Fluidmaster 400A fill valve is the most widely used toilet repair part in the US. It fits virtually every toilet made in the last 40 years and costs $10 to $14 at any hardware store. If your fill valve needs replacing, this is the one to buy — the package includes complete installation instructions.
DIY vs Plumber — Full Cost Comparison
| Repair Type | DIY Parts Cost | DIY Time | Plumber Cost | Your Savings |
|---|---|---|---|---|
| Float adjustment | Free | 2 minutes | $100 – $150 | $100 – $150 |
| Flapper replacement | $5 – $15 | 15 – 20 min | $150 – $250 | $135 – $245 |
| Fill valve replacement | $10 – $20 | 20 – 30 min | $150 – $300 | $130 – $290 |
| Complete toilet rebuild kit | $20 – $35 | 30 – 45 min | $200 – $350 | $165 – $330 |
| Full toilet replacement | $100 – $400 | 2 – 3 hours | $300 – $700 | $200 – $600 |
When to call a plumber: The water supply valve behind the toilet is corroded and cannot be turned off, the toilet tank has a visible crack, the wax ring seal at the base of the toilet is leaking water onto the floor, or the toilet rocks and is not firmly mounted to the floor. These issues go beyond tank internals and require professional repair.
Pro tip — buy the complete rebuild kit. For $20 to $35, you can buy a toilet complete repair kit that includes a new flapper, fill valve, and flush handle hardware. If your toilet is more than 10 years old and has been running, replacing all three parts at once saves you from another repair trip in six months when the next part fails.