Maintaining and Repairing a Cistern

How to keep your toilet cistern working

Once you understand the inner workings of a cistern it's easy to maintain it. Water is fed from the mains and enters the cistern via the inlet tube, which leads to the inlet valve. Connected to the inlet valve, or ball valve, is the float rod, or ball cock, and on the end of that is the ball valve float. When water enters the cistern, the ball valve starts to rise with the water level. When it reaches a certain level, the arm, or float rod, connected to the ball valve pushes against this inlet valve and begins to close it until the waiter flow is shut completely.

The handle on the cistern has a lever arm on the inside that operates a lift rod. The lift rod has a piston or a flap valve with plate below. When this flap valve is pulled up water rushes into the dome and through the inverted u-shaped siphon and then through the flush pipe. Siphon shapes vary from cistern to cistern.

Maintaining a Cistern

One of the most common problems with a cistern is the ball valve that gets stuck because of worn parts or from corrosion on the copper arm. Move it up and down to feel if there is some resistance and if so, the washers must be replaced with new ones. If the cistern keeps overflowing, the ball valve probably needs adjustment. A copper arm can be bent down little by little until the float can reach its highest position and shut the inlet valve properly. First check if the float itself is not damaged and filled with water.

If it's a plastic assembly the nylon nut on the ball valve must be adjusted, if there is one. Remember to tighten the lock nut again after the adjustment, but don't use too much force on a nylon nut. Pull the float rod upwards and if it keeps leaking then the diaphragm inside most probably is damaged and needs replacement. In older systems washers are used to stop the flow of water into the cistern, but modern models have a rubber diaphragm.

When you plan to replace an old ball valve you can just as well invest in a modern diaphragm valve. They are not expensive and are readily available. To install a diaphragm valve, first turn off the water supply to the cistern. It usually has a valve that serves it, but if not, then turn off the mains water supply. Flush the toilet to empty the cistern. Remove the entire float valve assembly from the cistern. Remove the ball from the old arm and fit it onto the new one and install the new assembly.

If the cistern doesn't fill up, check to see if the water supply to nearby taps is normal. If you push down on the ball float and the flow of water is slower than normal, then the filter in the ball valve could be clogged and must be cleaned.

What to do if water is leaking into the bowl

If water is leaking into the bowl, then the flap valve may be worn and must be replaced. To replace the valve, turn of the water supply to the cistern and flush the toilet. Use a sponge to soak up the remaining water. Remove the link that connects the handle to the lift rod. Disconnect the flush pipe and remove the siphon by unscrewing the large nut that holds it in place.

The flap valve can now be accessed. Replace the flap valve with a new one, reassemble the siphoning system and test it. Fill up the cistern again and test it with dye to see if water is still leaking.

If the cistern itself is leaking, it can be fixed with a sealant on the inside, while completely dry, until the cistern can be replaced. With bigger holes you could use epoxy or specialist putty to fill it from inside. If the toilet won't flush, it may be the lever arm that broke, so that the lift rod can't be lifted. The lever arm should then be replaced.

The best way to empty the cistern then - if needed - is to use cups and lastly a sponge.

Fixing a noisy cistern

If your cistern is noisy, it can be fixed by installing a silencer tube. It directs water from the inlet or float valve directly to the bottom for a bottom entry. Make sure it is permissible where you are residing, because there may be legislation against that. In the case of negative mains pressure, water can be sucked from your cistern into the water network. The exception is when a tube made from soft rubber or plastic is used, because it will collapse back on itself when siphoning occurs. Other noises could be caused by high water pressure. When it's too high, the float can bounce and send banging noises along the whole water system.

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