At some stage, all of us have the experience of water running into the toilet pan long after the toilet had been flushed. The first tell-tale sign for this is that water can be seen running down the inside of the pan and if this has been happening for a period of time, scale marks will appear on the porcelain caused by lime deposits in the water.

The second characteristic should you not be able to visibly see any sign of water running down the inside of the pan is a continuous hissing sound caused by the water passing through the float valve inside the cistern.

As soon as one of these signs are evident, the cause of the leak into the pan should be identified. The cause of this problem will be found in the cistern. Gently lift off the lid of the cistern and put it on a flat surface away from where you are working as these lids have the tendency to be in the wrong place at the wrong time.

Inside the cistern are two components to be found that is normally the cause of the leak in the toilet pan.

  • The flush valve – it has a rubber seal on the bottom part that lifts and opens up whenever the handle is pushed down allowing the stored up water in the cistern to flow through into the pan and wash away any deposits. The flush valve automatically resets back to the closed position once all the water is drained out of the cistern.
  • The float valve – it’s an automatic replenishing valve which allows water to fill up the cistern automatically once it’s being emptied. A buoyant float is connected to this valve that due to its buoyancy, stays afloat on the surface of the water. Once the toilet is flushed or the preset level of the water drops due to a leak, the float drops down with the water level causing the valve to automatically open up allowing water to fill up the cistern. Once the water level reaches the preset level, the float which is connected to an arm, causes a small rubber seal to be pushed into place shutting the orifice inside the ball valve through which the water flows.

Flush valve and Fill valve

The following picture shows water overflowing into the overflow tube of the flush valve making its way into the toilet pan.

Whenever you see the water overflowing into the overflow pipe, the following three things should be looked at.

  • Should the float valve have a ball (float ball) fastened to the arm of the valve, unscrew the ball from the arm and make sure that the ball does not have any water inside of it. Should water be found inside the ball, the ball will not stay afloat causing the float valve to stay in the open position letting water through continuously.

The solution to this problem – replace the float ball.

Toilet float ball

  • Should the float ball not be the problem, see whether adjusting the float valve arm will not solve your problem. If you have the float valve with a brass or aluminium arm connected to a float ball as indicated in the picture below, the arm can gently be bent downwards in order to adjust the water level. Once the adjustment has been made, drain a bit of water out of the cistern by flushing the toilet and allow the cistern to re-fill. If the flush valve closes off the water in time on the newly adjusted water level, your problem should be solved.

Toilet water level change

  • If your float valve doesn’t have an arm and ball float as described above, it most probably would be the kind that either adjusts by using a screwdriver to adjust the small float situated on the side of the valve upwards or downwards, or by manually adjusting the float as indicated on the side of the valve shown in the picture below.

  • Should all of the above mentioned not solve your problem, it is most likely that the small rubber seal inside the float valve has perished. You could go to your local plumbing supply store to try and find a new seal for your specific float valve but the chances are likely that you will be advised that they don’t stock the seals and you would have to replace the entire float valve. To replace the complete float valve – see the link below courtesy of The Homeowner Series.

If no water can be seen overflowing into the overflow pipe, your attention should be drawn to the remaining component called the flush valve. Flush valves come in a variety of different forms and shapes as some have the conventional toilet handle connected to the valve while others might have a flushing button situated on the top end of the cistern lid connected with a small cable to the flush valve. No matter the type of flush valve installed in your cistern, the main cause of a malfunctioning flush valve is more likely a perished rubber seal as indicated in the picture below.

These seals are readily available at your local plumbing supply and it would be advisable to take the old rubber seal along as a sample due to the different shapes and sizes.

Make sure before replacing the flush valve seal, that the seat which the seal pushes against to seal off the water is not pitted or cracked and that it is free from scale build-up. If there is some scale on the seat, gently remove it with a hard plastic object like the back end of an old toothbrush and fine steel wool.  Should pit marks or cracks be evident on the seat, it would be advisable to replace the complete flush valve.