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Plumbing Tips · Los Angeles & San Fernando Valley
Why Does My Toilet Keep Running?
A licensed plumber explains the 5 most common causes, how to diagnose the problem in 10 minutes, and when a DIY fix isn’t enough.
Quick Answer
A running toilet is almost always caused by one of five things: a worn flapper, a faulty fill valve, a float set too high, a corroded flush valve seat, or a tangled flapper chain. Most are simple DIY fixes costing $5–$20 — but left unrepaired, a running toilet wastes up to 200 gallons of water per day.
What You'll Learn
Is a Running Toilet a Big Problem?
That constant hissing or trickling sound from your toilet isn’t just annoying — it’s a sign that water is continuously leaking from the tank into the bowl, which means your fill valve is running non-stop trying to keep up.
The good news: most running toilets are caused by one of just five problems, and three of them can be fixed in under 30 minutes with a $10 part from a hardware store. The bad news: left alone, a running toilet can waste 4,000–15,000 gallons of water per month — and add $70–$200 to your Southern California water bill.
This guide walks through every cause, how to diagnose which one you have, what you can fix yourself, and when a plumber is the smarter call.
Diagnosing the Problem
The 5 Most Common Reasons Your Toilet Keeps Running
Over 90% of running toilet calls come down to one of these five issues.
What's Happening
The rubber flapper seals the tank bottom opening. Over time it hardens, warps, or collects mineral deposits and stops sealing, causing water to trickle continuously into the bowl.
How to Diagnose
Add 10 drops of food coloring to the tank. Wait 15 minutes without flushing. If color appears in the bowl, the flapper is leaking.
How to Fix
Turn off supply valve, flush to empty, unhook old flapper, snap in a new one. Match the brand at the hardware store.
✓ DIY — 15 min / $5–$15
What's Happening
The fill valve controls water into the tank after a flush. When it wears out it fails to fully close, causing a continuous hissing sound and constant water flow.
How to Diagnose
Lift the float by hand. If water stops, the float is set too high (Cause #3). If water keeps running with float lifted all the way up, the fill valve has failed.
How to Fix
Shut off supply valve, disconnect water line, unscrew old fill valve, install new one (Fluidmaster 400A is standard).
✓ DIY — 30 min / $10–$20
What's Happening
If the float is set too high, the water level rises above the overflow tube and drains continuously into the bowl, keeping the fill valve running non-stop.
How to Diagnose
Remove the tank lid and look for water flowing into the overflow tube (the open pipe in the center of the tank). If water goes in, the float is too high.
How to Fix
Turn the adjustment screw counterclockwise (new valves) or gently bend the float arm down (old ballcock style) until water stops at 1 inch below the overflow tube.
✓ DIY — 2 min / Free
What's Happening
The flush valve seat is the ring the flapper seals against. Hard water minerals and corrosion can pit this surface so even a brand-new flapper can't form a seal.
How to Diagnose
If you've already replaced the flapper and the toilet still runs, run a finger around the seat. A damaged seat feels rough, ridged, or uneven instead of glassy smooth.
How to Fix
Minor roughness can be sanded lightly. More often the entire flush valve assembly needs replacing — more disassembly involved.
⚠ Moderate — Consider a plumber / $15–$40
What's Happening
The chain connecting handle to flapper needs about ½ inch of slack. Too much slack and the chain gets trapped under the flapper. Too little and the flapper stays slightly open.
How to Diagnose
Remove the tank lid and check for kinks, tangles, or a chain so long it drapes under the flapper. Flush once and watch whether the flapper closes completely.
How to Fix
Reattach chain to a different link to get ½ inch of slack. Cut away excess chain if needed.
✓ DIY — 2 min / Free
The Real Cost of Waiting
How Much Water Does a Running Toilet Waste?
A running toilet is one of the most wasteful plumbing problems in any home — and one of the easiest to ignore because the water goes straight down the drain.
At LA Department of Water & Power rates, a toilet leaking 200 gallons per day adds approximately $70–$150 to your monthly water bill. Over a year, that's 73,000 gallons and $840–$1,800 in wasted water — for a problem a $10 flapper could have fixed on day one.
Do This Before Anything Else
How to Diagnose a Running Toilet in 10 Minutes
Follow these steps in order. You'll identify the exact cause before touching a single part.
Remove the Tank Lid and Listen
Is the water running continuously, or does it run briefly every few minutes? Continuous running suggests a fill valve or float issue. Intermittent (phantom flush) almost always points to a leaking flapper.
Check the Flapper Chain First
Confirm the chain has about ½ inch of slack and isn't caught under the flapper. Takes 10 seconds.
Chain tangled or too short/long? Adjust it → test flush → done.Check Water Level vs. Overflow Tube
Is water flowing into the tall center tube? The water level should sit about 1 inch below the top. If water goes in, adjust the float down.
Water going into overflow tube? Lower the float → water stops → done.Do the Food Coloring Test
Add 10–15 drops of food dye to the tank. Wait 15 minutes without flushing. If color spreads into the bowl, the flapper is leaking.
Color in bowl? Replace the flapper. Bowl stays clear? Problem is fill valve or float.Test the Fill Valve with the Float Trick
Lift the float all the way up by hand. If water stops, lower the float setting. If water keeps running with the float fully raised, the fill valve has failed.
Still running with float lifted? Replace the fill valve.Check the Flush Valve Seat
If you've already replaced the flapper and the toilet still runs, run a finger around the seat. Roughness or pitting means the seat is damaged and needs replacing.
Rough or pitted seat? Call a plumber for flush valve replacement.DIY Guide
Easy Fixes Ranked by Difficulty
Start with the easiest options first. You may not need tools at all.
1. Adjust the Flapper Chain
Move the chain to a different link on the handle arm until there is about ½ inch of slack. Flush to test. If the flapper won't seal, the chain is still the issue.
2. Lower the Float Level
If water runs into the overflow tube, adjust the float down so the tank fills to 1 inch below it. Turn screw counterclockwise (new valves) or bend float arm down (old ballcock).
3. Replace the Flapper
Turn off supply valve, flush to empty tank, unhook flapper from overflow tube pegs, disconnect chain, snap in new flapper, reattach chain with ½ inch of slack.
4. Replace the Fill Valve
Turn off supply valve, flush, place towel under tank. Disconnect supply line, unscrew locknut, lift out old valve, install Fluidmaster 400A, reconnect supply line.
Know Your Limits
When to Stop DIYing and Call a Plumber
Some running toilet problems go beyond a flapper or fill valve. Here are the signs it's time to call a pro.
Still Running After Replacing Both Parts
If you've replaced the flapper and fill valve and it still runs, the flush valve seat is likely damaged and needs a plumber.
Water Pooling at the Base
Water on the floor signals a failed wax ring or cracked base — a repair that requires removing and re-setting the toilet.
Supply Valve Won't Shut Off
If the shut-off valve is corroded and won't turn, you can't safely do any repair. A plumber will replace the valve and fix the toilet in one visit.
Crack in Tank or Bowl
A cracked tank or bowl cannot be permanently repaired — the toilet needs replacing before water damage spreads to the subfloor.
Toilet Is 15–20+ Years Old
Multiple worn parts at once often make replacement more economical than repairs. Modern toilets also use 60% less water per flush.
Toilet Rocks When You Sit
A rocking toilet means the wax ring has failed. Combined with a running toilet, this can quickly damage the subfloor.
Michael's Valley Plumbing — Same-Day Toilet Repair
We fix running toilets, wax ring failures, cracked tanks, and full replacements across LA & the San Fernando Valley.
Toilet Still Running? We Fix It the Same Day.
Michael's Valley Plumbing serves Los Angeles and the San Fernando Valley. We carry flappers, fill valves, and wax rings on every truck — most running toilet repairs take under 90 minutes.
Keep It Running Right
How to Prevent Your Toilet From Running Again
A few simple habits and a $15 investment prevent 99% of running toilet problems.
Upgrade to a Long-Life Flapper
Standard rubber flappers last 4–6 years. Silicone or Fluidmaster PerforMAX flappers resist LA's hard water and last twice as long.
Do the Dye Test Once a Year
2 minutes and a few drops of food coloring. Catching a slow flapper leak early prevents a $100+ water bill surprise.
Schedule an Annual Plumbing Check
A plumber inspects the flapper, fill valve, and supply line in under 10 minutes. Proactive replacement costs far less than an emergency call.
Install a Smart Leak Detector
A $15–$30 water sensor near the toilet base alerts you immediately if water appears on the floor — before it soaks the subfloor.
Use a Water Softener or Filter
Hard water accelerates mineral buildup on flappers and valve seats. Most LA homes have hard water — a filter extends part life significantly.
Consider a Low-Flow Replacement
Toilets 15+ years old use 3.5–7 gallons per flush. Modern WaterSense toilets use 1.28 gpf and often pay for themselves in water savings within 2–3 years.
Frequently Asked Questions
Why does my toilet run intermittently (phantom flush)?
▼Phantom flushing is caused by a slow water leak from the tank into the bowl. As the water level drops, the fill valve kicks on to refill. The culprit is almost always a worn flapper. The food coloring test confirms it in 15 minutes.
How much water does a running toilet waste per day?
▼A running toilet wastes between 30 and 500 gallons per day. A slow trickle wastes 30–50 gallons. A typical running toilet with a worn flapper wastes around 200 gallons per day. A severe case with a failed fill valve can waste 400–500 gallons daily.
Can a running toilet significantly increase my water bill?
▼Yes — and often dramatically. A toilet running 200 gallons per day adds roughly 6,000 gallons to monthly usage. In Los Angeles at LADWP Tier 2 rates, that's an extra $70–$150 per month. Many homeowners call us after an unexplained bill spike and discover a running toilet was the cause.
How do I know if my flapper needs replacing?
▼The most reliable test: add 10 drops of food coloring to the tank. Wait 15 minutes without flushing. If color appears in the bowl, your flapper is leaking. Visually, a failing flapper looks discolored, warped, or feels brittle instead of soft and flexible.
How much does it cost to fix a running toilet in Los Angeles?
▼A DIY fix costs $5–$30 in parts. Professional toilet repair in Los Angeles typically runs $75–$200 depending on what needs replacing. Most running toilet calls are resolved in one visit for under $150 at Michael's Valley Plumbing.
Can I fix a running toilet myself?
▼For the three most common causes — worn flapper, high float, or tangled chain — yes, most homeowners fix it in under 30 minutes. Fill valve replacement is also manageable for a confident DIYer. Flush valve seat damage, cracked tank, or a stuck supply valve are better left to a licensed plumber.
How long does professional toilet repair take?
▼Most running toilet repairs at Michael's Valley Plumbing take 30–90 minutes in a single visit. Our trucks carry flappers, fill valves, wax rings, and supply lines — we diagnose on arrival, provide an upfront quote, and finish the same day.