Toilet Won’t Stop Running: Causes and Easy Fixes

When a toilet won’t stop running, it’s one of those things that’ll drive you mad, and it’s costing you money. I’ve been asked about this so many times, both as a tradesperson and a writer. Fortunately, it’s one of the easiest things to sort out yourself. You probably won’t need to call anyone. Most of the time.

Title: How to fix a running toilet. The two most common causes. Upload Date: April 29, 2022 Description: A practical walkthrough of the two most common causes of a running toilet with instructions on how to adjust or repair the problem yourself. Video Credit: JENSEN DIY

What’s happening inside the cistern

Here’s what’s happening in your cistern. Every time you press the button, a chain or lever lifts the flapper valve at the bottom of your cistern. The water flows from the cistern to the bowl, the valve drops back down, and the fill valve refills the cistern. The water rises to a certain level, then a float tells the fill valve to turn off. Somewhere in that process, something’s gone wrong and the toilet water keeps running. In my experience, 90% of the time it’s either the flapper valve or the fill valve at fault. Every now and then it’s the overflow or the chain length, but that’s fairly rare.

Person repairing toilet tank using wrench, replacing internal fill valve components in bathroom.

The flapper valve — the most common culprit

If your toilet won’t stop running, this is usually the culprit. The flapper valve is the rubber disc at the bottom of your cistern that covers the hole between the cistern and the bowl. Over time, this valve can distort or crack, or a buildup of minerals means it doesn’t seal properly. Here’s what you do. Turn the water off to the toilet. There should be a tap at the back of the toilet, or under the cistern. Flush the toilet to empty the cistern, then look at the flapper. If it feels stiff or rough, or you can see cracks, you need a new one. They’re $10 to $20 at the hardware store and they take 5 minutes to fit. I’ve done hundreds of these over the years and it’s still one of my favourite DIY fixes. You go from an annoying hiss to silence in less than 10 minutes.

Plumber holding a new fill valve assembly and adjustable spanner while repairing a toilet cistern

When the fill valve won’t turn off

If the flapper valve looks okay, your problem is probably the fill valve. This is the tall contraption on the left-hand side of your cistern (if you’re standing behind it). Its job is to fill the cistern after you flush, then turn off when it reaches the right height. A faulty fill valve won’t switch off when the float tells it to, and the toilet water keeps running well past where it should stop. You might notice the water level in the cistern is higher than the top of the overflow pipe. That’s usually the giveaway. Some fill valves have an adjustable float; there’s a screw at the top that you can turn to lower the water height. Try that first. If the adjustment doesn’t work, you’ll need to replace the fill valve assembly. It’s not as technical as it seems. A new valve will cost anywhere from $15 to $30, and it usually comes with straightforward instructions. All you need is an adjustable spanner and 20 minutes.

Inside view of a toilet tank showing the float mechanism, overflow tube and flush valve with red cap

The overflow tube and other less obvious causes

Sometimes it’s not your flapper valve or fill valve. The overflow tube (the vertical pipe you see in the middle of the cistern) has an ideal height for a reason. If the water level is too high, it’ll constantly flow down the overflow tube and into the pan. This can sound like a faulty flapper. Sometimes it’s the chain length. If the chain that links your flush button to the flapper is too short, it can’t sit properly on the seal. Too long and it can get caught under the flapper itself, keeping it partially open. Adjusting the chain length is a free repair. Just move the clip. Buildup around the flapper seat can also cause leaks. Get some white vinegar and an old toothbrush and give it a good scrub.

Professional plumber in blue uniform kneeling beside a toilet with tools while repairing the cistern

When to get a plumber and when to replace parts

Knowing how to stop toilet from running is one thing, but there are times when a licensed plumber is better. If you’ve replaced your flapper and fill valve and it still leaks, you might have a crack in the cistern or something further down the line. Don’t keep buying parts if it’s something more serious. If you do need parts, buy decent ones. Those ultra-cheap cistern internals you see from no-name brands will only last a year or two. Find a reputable Australian supplier that sells genuine wc cistern parts and toilet cistern components with a decent warranty. It’s the difference between a once-off repair and a yearly one. Here’s something nobody thinks about. A running toilet can waste up to 26,000 litres of water per year. 26,000! But it’s not just toilets. Leaking taps, urinals in commercial premises and leaking pipes all wastewaters. Fixing that running cistern is one of the simplest ways to lower your household water bill.

FAQs

Will a running toilet really increase my water bill?

Yes! A toilet that runs constantly can add hundreds of dollars to your annual water bill, depending on the leak. Even a slow leak will add up over time. Fix it ASAP.

Is it okay to turn off the water supply to my toilet?

Yes, it’s perfectly safe. The isolation valve behind (or below) your toilet only controls the water supply to your toilet. You can turn it off without affecting any other fixtures or appliances in your home. I recommend turning it off while you investigate your running cistern.

How often should I replace the internals of my toilet cistern?

Most flapper valves will only last 3 to 5 years, depending on your water quality. Fill valves can last up to 10 years. If you live somewhere with hard water, you might need to replace them more often because of mineral buildup. Inspect them every year.