How to Fix a Toilet Cistern That Won't Stop Filling

It's usually quite easy to tell when your toilet cistern won't stop filling up, often it's either the sound of constant hissing or trickling, or water constantly overflowing down the external overflow tube and flowing outside or through the internal overflow and into the toilet pan.

It is always recommended to fix this issue as soon as it arises as it can result in a large amount of wasted water over time, and if you're on a water meter, you may end up with a very expensive bill.

If your toilet cistern won't stop filling, this is almost always a sign that there's something wrong with your cistern inlet / float valve. This is the part that is responsible for filling the cistern. 

If your inlet valve won't shut off properly it could very well be that the diaphragm washer inside of the valve needs to be replaced. Over time as the valve is continuously opening and closing, small tears can start to form in the diaphragm washer, in turn the diaphragm washer will no longer give a good seal.

Any debris in the water supply (which can be commonly caused by nearby work being carried out on the water supply) can also contribute overtime to this washer being worn.

Many make the mistake of purchasing a full replacement inlet valve at the first sign of any issue, replacing just this washer may save you a lot time and money in the long-term. We advise purchasing a couple of these washers at a time so you've got one readily available in the event that the washer fails again in future.

If a diaphragm washer doesn't fix the problem or no replacement diaphragm washers are made for your particular model of inlet valve, then a replacement inlet valve will need to be installed.