How to stop toilet running once full?

[Kalliste]

Recently my toilet has started running all the time even when it's full. This overflows into the bowl and only stops once the water is turned off.

I'm not sure of the brand of toilet, it doesn't appear to mention it anywhere. The house is about 15 years old though.

How the toilet looks inside. Side note: Can anyone tell me why one side is clean and one side isn't?

How the overall toilet looks

Video of toilet filling from flush

[JacobZ]

Hi @Kalliste,

A warm welcome to the Bunnings Workshop community, it is fantastic to have you with us.

It sounds like your toilet's flush valve (outlet valve) isn't sealing properly, allowing water to continuously leak into the bowl. Since the cistern is constantly emptying, it is also constantly filling to counteract this. This is usually caused by a worn-out or misaligned seating washer, which can harden or become damaged over time. If the flush valve itself isn’t sitting correctly or is worn out, it may not be sealing properly, leading to a constant flow of water. Another possibility is debris or limescale buildup preventing a proper seal.

To fix the issue, start by turning off the water and flushing the toilet to empty the cistern. Inspect the seating washer at the base of the outlet valve—if it looks worn or damaged, replacing it with a new seating washer should solve the problem. Clean any debris or limescale buildup around the valve, as even small particles can interfere with the seal. If replacing the washer doesn’t fix the problem, a full outlet valve replacement may be necessary.

As for why one side of the toilet bowl is cleaner than the other, this is usually due to the way water flows into the bowl. The side receiving more direct water flow, which in your case is the side closest to the inlet valve, stays cleaner, while the other side accumulates grime or mineral buildup over time. This is a common occurrence, especially if the water doesn’t circulate evenly around the bowl. 

Let me know what you think, and if you have further questions, please don't hesitate to ask.

Jacob

[Jason]

Hi @Kalliste,

Let me also extend a very warm welcome to the Bunnings Workshop community. We look forward to reading about all your projects and plans for around the house and garden.

I trust you found Jacob's reply helpful. 

Just wanted to add that we have a step-by-step guide How to fix a leaking toilet that you can also consult for assistance.

Please let us know how you go.

Jason

[Kalliste]

Thanks for your speedy response Jacob.

With the seating washer, is there any way I can tell which one I need or are they much the same?

[JacobZ]

Hi @Kalliste,

Do you know what brand and model of cistern you have? 

This is often the best way to work out what seating washer you require. If you can find the brand and model and let me know, I'd be happy to check for you. There is often an identifying tag on the inside of the cistern.

If you don't have any luck, then removing the old washer and bringing it in-store to compare is another way. I'm sure the team at your local store would be happy to help match it  up with a suitable replacement.

Let me know how you go.

Jacob

[Kalliste]

Thanks for the guide Jason.

I'm going to be grabbing the parts this week. I was just wondering in the guide it mentions:

"If water is leaking from the cistern to the pan, it is leaking from the flushing valve. If the leak stops when the cistern tap is turned off, the leak is coming from the inlet valve."

For me, the leak stops when the cistern tap is turned off and the cistern stays full. Does this mean I should actually be replacing the inlet valve seal rather than the seating washer? Or should I just do both?

Thanks!

[JacobZ]

Hi @Kalliste,

Apologies for that, I missed that key bit of information.

If the water stops when the cistern tap is turned off, then it is likely an issue with the inlet valve.

With that information, it seems like the best place to start is by replacing the inlet valve seal. Step 4 in How to fix a leaking toilet will guide you through the replacement process.

If you find that the leak persists, you can then replace the seating washer.

Let me know how you go.

Jacob