How to Fix a Running Toilet: Valves, Cisterns, and Drains

The running toilet is one of those issues that get put off for far too long. You hear the water running, or perhaps the cistern is filling on its own and no one has used it. You think that it will just fix itself. It won’t. If you need to know how to fix a running toilet, then in most cases it is a simple fix that does not require a plumber. Every day you leave it is money and water down the drain, so act sooner rather than later.

Why Your Toilet Won’t Stop Running (and What Is Going On Inside)

To fix the issue you first need to understand what is happening in that cistern. There are two components that control the water in your toilet. The fill valve and the flush valve. The fill valve is the valve that allows water into the cistern when you flush. The flush valve includes the rubber flapper in the bottom of the cistern that opens when you push the button.
When your toilet running constantly, it is usually one of these two parts. Either your fill valve is not turning off all the way, or your flapper is not sealing, and you have a leak into the toilet bowl. Or, the water level is set too high and it is running into the overflow tube. I have seen all three of these issues literally hundreds of times and the fix usually takes less than 30 minutes.

Fixing the Fill Valve (the Valve That Controls the Water Level)

If you remove the lid from your toilet, and the water level is above the overflow tube, or you can hear the fill valve humming, then you know that the fill valve is your problem. Here is how to fix a running toilet if the fill valve is the issue.
Shut off the water supply at the valve behind the toilet and flush the toilet to empty the cistern. Most modern fill valves have an adjustable float. Either a float arm with a float ball on the end, or a float cup that moves up and down the valve. If the float is set too high then the water level is above the overflow tube, and the fill valve never shuts off. Simply adjust it down so that the water level is about 25mm below the top of the overflow tube.
If adjustment won’t fix it, then the fill valve is simply worn out. New ones are cheap, you unscrew the old one from the bottom of the cistern, put the new one in, hook the water line back up and away you go.

When the Flapper or Flush Valve Is the Problem

The other common issue is the flapper, the rubber disc that covers the flush valve opening in the bottom of the cistern. Over time, flappers can become warped or mineralised, preventing a proper seal, which causes the toilet to run. You may also notice your toilet not filling with water the way it should; that is because the water is seeping from the cistern into the toilet bowl from the faulty flapper, and the fill valve is trying to compensate by running constantly. To check, add a few drops of food colouring to the cistern and wait 20 minutes without flushing. If the coloured water has made its way to the bowl, you have a bad seal. Stop the water supply at the isolation valve, flush the toilet, unhook the chain from the old flapper, and attach the new one. A new flapper shouldn’t cost you more than $10, and they’re universal for most toilets.

Other Common Toilet and Drain Problems

Now that you know how to fix a running toilet, you might feel more empowered to tackle other simple plumbing problems, such as learning how to unclog a drain. There’s nothing worse than calling out a plumber for a problem that can be fixed with a simple plunger or drain snake. If you’ve determined that you need to replace your fill valve, look for a quality toilet float valve that matches your cistern type. Older cisterns use a ball-float inlet valve, while newer models typically use a compact toilet bowl fill valve with an integrated float cup. For flappers, flushing mechanisms, and other parts, a good range of wc parts will cover most standard Australian toilet models. Ninety percent of running toilets can be fixed with $15 parts and some basic tools; the other ten percent require a plumber, typically because the cistern is cracked or the flush valve seat is corroded.