Repair cistern float - this is how it works!

In the cistern of each toilet there is a so-called float, also filling valve called. It makes no difference whether the cistern was flush-mounted or surface-mounted. The float has the task to fill the cistern with water. As the water runs into the cistern, the float detects the water level and stops the water supply as soon as the water level reaches a certain level. Now, when the toilet flushing is activated, the float sinks, opens the float valve and refills the cistern with water again. Over time, however, it may happen that the filling valve does not close properly and therefore always runs after water in the cistern, until it finally overflows. Limescale deposits on the filling valve are often responsible for this.

If the leaking toilet flush goes unnoticed for some time, a sinfully high water bill threatens in the worst case.

How does a filling valve in the cistern?

If you operate the flushing of the toilet, the water that is in the flushing cistern will be leveled out to avoid unnecessary costs this flushed directly into the toilet. While the water in the cistern becomes less and less, the float lowers at the same time. The float is attached to the end of a linkage, which is finally connected to a valve. If the float sinks, the valve is opened immediately and fresh water can flow into the cistern and the water level in the cistern rises again over time. When the water has reached a certain level, the float gets buoyancy and the valve is closed again. So that the float is pushed at all by the rising water, this is usually made of rigid foam (Styrofoam). In newer cisterns, however, a hollow body is installed. In order to prevent contaminated water from entering the water circuit of the mains network accidentally, a special pipe interrupter is installed in the float valve to prevent backflow.

What to do if the valve does not close?

As soon as you notice that There is more water in the cistern of the toilet than it should be, for some reason it overflows too much water. The reasons can be quite diverse in general. For example, in some cases the swimmer may not be working properly. Especially in older cisterns is still often a float made of styrofoam, which can fill with the years of aging more and more with water until he eventually gets no more buoyancy and the valve is no longer closed. In addition, it may happen that the float is stuck. If this is indeed the case, it may already help to adjust the boom a little so that the swimmer can move freely again.

What to do if water is constantly flushed?

As soon as more Water in the cistern runs as usual and this may even be flushed over the overflow into the toilet, you should open the cistern and look at the whole thing from the inside. This usually already indicates where exactly the problem lies. Does the water actually over the overflow into the toilet, then either the rod of the float is jammed or the swimmer does not get enough lift, because he has been soaked with water over the years. If, on the other hand, water is constantly running from the cistern into the toilet, but not over the overflow, the problem is a bit deeper, namely at the lifting bell.

If it is actually on the bell, then you should now turn off the water inlet to the cistern and then operate the toilet flushing, so that all the water from the cistern runs. Now turn the bell a little to the left and loosen it. Now lift the bell out and release an annular seal. It may be cracked, and you should replace it with a new one. On the other hand, if it is only calcified, it is sufficient to decalcify the seal. Then put the gasket back into the cistern, put the bell back on and open the water supply again. Whether the repair has helped will show up when no more water goes into the toilet without the flush being activated.

Another reason that can cause too much water to run into the cistern is, however, also possible be a calcified valve. Lime deposits will no longer completely close the valve when there is enough water in the cistern. In this case you should immediately descale the entire float valve. But it can also be that a seal breaks at the valve as well. However, this can usually be easily replaced. The cost is usually a few cents. However, if this does not help, then you will inevitably have to install a new float valve, such as one from Geberit.

How can I decalcify the float valve?

To decalcify the float valve or gaskets, you can use various means. such as

  • Kalklösetabs
  • Vinegar
  • Vinegar Essence
  • Citric Acid

Just put one of these home remedies directly on the valve and let it work for a few hours.

In some regions, the lime content is much higher in the water than in others. Depending on how hard the water in the pipes is, the faster the float valve can calcify. Make sure you descale and decalcify the entire cistern at regular intervals according to the water hardness.


If the water in the toilet cistern simply does not want to stop running, this can be due to a variety of causes. In many cases, the swimmer is the reason. If the linkage is tilted, then this can easily be solved again. On the other hand, if the swimmer is under water, then he is probably soaked in water and must be replaced.

Artikelbild: © Dave Willman /