The short answer
A toilet making noise in a Northern Virginia home is almost always telling you which part is wearing out. A hiss after it fills is water slipping into the overflow tube or past the flapper. A whistle or a foghorn hum while it fills is a worn fill valve or high water pressure. A bang when it stops filling is water hammer. A gurgle in the bowl when another drain runs is a drain or vent problem, not the toilet. And a short refill when nobody flushed is a slow leak called a phantom flush. Most of these are a part, not a new toilet.
Match the sound
Swipe to see all columns →
Swipe to see all columns →
| The sound | When | Usually | First thing to try |
|---|---|---|---|
| Hissing | After the tank fills, or all the time | Water running into the overflow tube, or a fill valve that won’t fully close | Lower the float an inch. Still hissing? Replace the fill valve. |
| Short refills, nobody flushed | Every few minutes to every hour | The flapper leaking into the bowl | The 10-minute dye test, then a new flapper |
| Whistling or a foghorn hum | While the tank fills | An old fill valve, or high water pressure | Replace the fill valve. Check the pressure if it comes back. |
| A bang or a thud | Right when the tank stops filling | Water hammer, often from high pressure | Check the water pressure |
| Gurgling in the bowl | When a sink, tub or washer drains | A partial clog or a blocked vent | Plunge once. If other drains gurgle too, it’s the line. |
| Trickling behind it | Any time | The supply line or the shutoff valve | A towel under it, and call |
| Running that won’t stop | After a flush | A flapper stuck open or a fill valve stuck on | Turn the water off at the valve behind the toilet |
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Hissing
Take the lid off and look at the overflow tube, the open pipe in the middle of the tank. If water is running into the top of it, the tank is filling too high and the fill valve never gets to shut off. Most fill valves have a clip or a screw on the float. Set it so the water stops about an inch under the top of the overflow tube, flush, and listen. If the level is right and it still hisses, the seal inside the fill valve is worn. That’s a replacement, not an adjustment.
If the hiss comes and goes, a few seconds at a time, that’s the fill valve topping up a tank that’s leaking into the bowl. Toilet refills by itself covers that one start to finish.
Whistling, squealing or a foghorn hum
An old fill valve, especially a ballcock with a float ball on an arm, whistles as its washer wears and the water squeezes past it. The sound carries through the whole house when someone flushes at 2 in the morning. A new fill valve is quiet and a quick swap. If the toilet is newer and still whistles, check two things: the shutoff valve behind it should be all the way open, since a half-closed valve can whistle, and the house water pressure may be too high.
A bang in the wall when it stops filling
A thud in the wall right as the tank finishes filling is water hammer. Water moving through the pipe stops all at once when the fill valve closes, and the pressure wave knocks the pipe against the framing. Dishwashers and washing machines do the same thing. It’s worse when the house pressure is high, and water off the main in parts of Northern Virginia runs well over 100 psi, which is why so many houses here have a pressure reducing valve where the water comes in. When that valve wears out, every fixture in the house gets street pressure. A pressure gauge from the hardware store, screwed onto an outdoor spigot, tells you: over 80 psi is too high.
Pressure reducing valve explains the overnight test and the fix. A pipe that knocks can also be strapped where we can reach it.
Gurgling
A toilet that gurgles or bubbles when a sink, tub or the washer drains has a drain or vent problem, not a bad toilet part. Air is being pulled through the toilet’s trap, either past a partial clog in the line those fixtures share or because the vent pipe on the roof is blocked. Why is my toilet gurgling goes through the causes and what to try first, and one drain or the main line tells you how far the clog goes. If it also flushes slow, it’s the same problem.
Trickling or dripping behind the toilet
Water noise from behind the toilet, with the tank quiet, is usually the supply line or the shutoff valve. Run a dry paper towel along the line from the valve to the tank. A drip at a nut can often be stopped with a quarter turn. A plastic line that’s bulging, or a valve weeping at the stem, should be replaced soon. Those are the parts that let go all at once and flood a floor.
Running that won’t stop
If it’s running full force after a flush, lift the tank lid and push the flapper down. If that stops it, the flapper or the chain is the problem. If water keeps pouring in and over the overflow tube, lift the float and hold it. If that stops it, the fill valve is stuck. Either way, turn the shutoff valve behind the toilet clockwise until it stops, and the toilet is safe until it’s fixed. Toilet keeps running has the step-by-step repairs. Water on the floor and a valve that won’t close? We run 24/7 emergency plumbing.
Why it matters on the water bill
Every one of these, other than the gurgle and the bang, is water going down the drain that you pay for twice, once as water and again as sewer. A toilet that hisses all day can run hundreds of gallons. What a running toilet adds to your water bill puts it in dollars, and why is my water bill so high covers the rest of the house.
Fix it small, fix it now
A leak caught early is cheaper three ways. The water and sewer bill stops climbing. The water stops soaking the subfloor or the ceiling under it. And it stays a small repair, a part and an hour, instead of a bigger one later. Most of what we find behind a noisy toilet is repairable, and once it’s fixed right, you stop listening for it at night.
What it costs when we fix it
Most running and noisy toilets are a repair, toilet repair at $250 to $900, with the price in writing before we start. When the toilet itself is worn out, a new one installed runs $800 to $1,300, and this month’s coupons on our offers page take $100 off a new toilet, or $50 off any plumbing repair over $400. Any plumbing repair also comes with a whole-house plumbing inspection, a $149 value. If the water is going somewhere other than a toilet, leak detection runs $200 to $500. A plumbing diagnosis visit is $49, or $250 after hours.
Call (703) 997-9757, day or night, or book a toilet repair online. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why is my toilet making a hissing noise?
Water is running into the overflow tube because the tank fills too high, or the fill valve isn’t closing. Lower the float an inch. If it still hisses, replace the fill valve.
Why does my toilet make noise when nobody flushed it?
The tank is leaking into the bowl and the fill valve is topping it up. It’s usually the flapper. A few drops of food coloring in the tank confirm it.
Why does my toilet whistle when it fills?
An old fill valve with a worn washer, a shutoff valve that’s only partly open, or high water pressure. A new fill valve fixes most of them.
What causes a bang in the wall after flushing?
Water hammer. The fill valve closes, the moving water stops all at once, and the pipe knocks. High water pressure makes it worse, so check the pressure.
Is a gurgling toilet a problem?
It’s a drain or vent problem, not a toilet part. If other drains gurgle too, the line they share is partly clogged and should be cleared before it backs up.
