Toilet Cisterns

The modern toilet cistern is piston actuated; older patterns used a bell-type mechanism which did not normally require attention, other than possible adjustment to the ball valve. This pattern is easily recognised by its belled central dome.

If a ball float becomes perforated or the washer on the outlet is faulty, both patterns of cistern may overflow.

The piston siphon is more efficient. When the flushing lever is depressed or WC cistern the chain pulled, a disc or plunger in the siphon enclosure rises, forcing the water above it and down the flush pipe to the toilet pan.

In the flush pipe, a partial vacuum is created which is sufficient to siphon off the water in the cistern. The disc is perforated, allowing water to flow through it from the cistern.

It is closed by a plastic flap or washer on the initial up-stroke. The flap acts as a non-return valve and if distorted or punctured, the flushing section may fail or be impaired.

To change the washer on a piston cistern, first flush the cistern and tie up the ball float arm to shut off the flow of water. Bale out or mop up with a cloth any residue of water remaining.

Unlock the nut beneath the cistern which secures the flush pipe to the siphon. On some plastic cisterns this nut is only hand tight. If a spanner is needed, this can be used to uncouple the larger nut holding the siphon to the base of the cistern.

Check when replacing the siphon that the joint between it and the cistern is in sound condition.

Replace any worn washers and apply a smear of non-toxic jointing compound to ensure a watertight joint.

Remove the flush-lever linkage; normally, it can be lifted out bodily. Take out the siphon and remove the plunger disc from the base of the dome; take off the small retaining washer which holds the valve washer in place. Replace this with one of an equivalent size. If a replacement is not available, you can make one by cutting a disc of heavy PVC sheeting, using the old washer as a template.

Now the unit can be reassembled, once you have checked that the connections at the base of the cistern are satisfactory. Release the valve arm and allow the cistern to refill.

Ball valves

The method of replacing or repairing a faulty ball valve, or ‘float’, is the same for both a cold-storage cistern or a WC.

Usually, worn washers, perforated floats, eroded seatings, lime deposits or grit on moving parts are the causes of trouble and correction does not involve physical removal of the cistern connections.

If replacement of the mechanism does become necessary, check that a similar inlet valve is used in replacement-high, low or medium pressure, in accordance with the water supply.

Supply to the cistern must be shut off when maintenance or replacement is carried out. If the ball float is perforated it will become waterlogged and sink and the cistern will overflow continuously.

A new ball float is simply screwed on to the threaded spindle at the end of the float arm. A perforated ball can be temporarily repaired by first tying up the arm, removing and draining it. The ball can then be encased in a polythene bag, with the neck of the bag tied over the lever arm.


A faulty valve washer may also cause a continuous overflow. Worn valve seatings can be reground, as with a tap, but capping with a nylon seat or replacement of the unit is not expensive.

Replacing a faulty washer entails removing the cistern lid or cover and extracting the split pin securing the lever of the piston, enabling the piston to be removed. On some types you may first have to remove the cap on the end of the cylinder.

To do this use a wrench to uncouple the washer retaining cap; the piston will then detach into two halves. If there is grit behind the valve seating flush this clear before replacing the valve.

Air locks

Air locks in modern plumbing systems are rare. These are most likely to occur after refilling following repair-and-maintenance work. The most common problem is the air lock, caused when a volume of air is trapped between two bodies of water in a pipe-usually where it changes direction from up to down.

The mains pressure is usually sufficient to force the entrapped air bubble to the nearest tap or valve where it is easily released.

A more difficult type of air lock to clear is one where the pipe is fed from the cold-storage cistern. This is because of its much lower head of pressure. To clear such an air lock, connect the low-pressure storage side to the high-pressure mains.

Join the appropriate taps with a piece of hose. Leave a tap or ball valve open on the blocked side to allow the air to escape when the two taps are turned on.

Where the air lock is on the hot-water side, temporarily block off the vent pipe above the cold cistern-but remember to unblock the vent once the lock is cleared.

Where there are frequent air locks, check the routing of pipes with a view to modifying them to eliminate possible tortuous runs of pipework. It may be necessary to fit air-release valves at points where air locks persistently occur.

10. November 2011 by admin
Categories: Featured, Handyman Tips | Tags: , , , , , , , , , | Comments Off on Toilet Cisterns


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