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Lavatory cisterns - common problems

Lavatory cisterns are usually very reliable, but occasionally problems arise, this article deals with these. When a problem becomes apparent, ask yourself if the problem suddenly appeared, has it gradually got or has the problem always been there ?, the answer should help you identify if something has just broken, become worn or possibly if something is incorrectly installed - this will allow you to discount some possible causes.

One thing to note is that cisterns are matched to the pan, if they are not matched, problems are likely to be encountered.

Cistern does not flush properly when operated:

  1. If a cistern with a syphon type flush has never flushed properly, the most likely problem is that the water level is too low - the water should be about 12mm (half inch) below the level of the overflow outlet. To raise the water level, the height of the float needs to be adjusted, the method of achieving this depends upon the type of valve/ball fitted:
    • On some arms between the valve and float, there is a hinge along the arm, usually with a lock screw or nut - to adjust, loosen off the lock screw/nut and adjust the hinge to raise the float.
    • Other float arms incorporate an adjustment screw at the valve end (usually with a lock nut), release the lock nut and unscrew the adjustment screw to raise the float.
    • Another alternative arrangement is where the arm between the valve and float is a solid brass rod; with this arrangement, the rod itself needs to be physically bent. To do this without putting undue pressure on the valve,grip the rod firmly in both hands, don't move the hand near to the valve and adjust the rod by using the other hand to bend the rod up a small amount - this will raise the float.
  2. If a cistern with a syphon type flush fails to flush and the water level is correct, it could be that the flexible diaphragm in the syphon has become worn and can no longer raise enough water into the syphon to get the water flowing; there will be nothing visible within the cistern to confirm this, it will probably have become worse over time and sometimes the cistern may work if the flush is operated with a sharp motion. The flexible diaphragm can be replaced, replacements should be available at good DIY or hardware stores, but it does involve removing the syphon from the cistern. - details and illustrations are shown on this page.
  3. If the flush suddenly fails completely, it could be that the link between the handle (or chain) and the syphon has become detached inside the cistern - this would be quite obvious as the handle/chain will have lost its normal 'feel' - e.g. the handle/chain will feel loose and won't return after operating. Usually, the top of the cistern can be lifted off and the detached linkage will be obvious it just needs to be reattached and then retightened to avoid it becoming detached again - tightening the linkage may involve using a pair of pliers to bend a wire loop so it cannot come of again, or retightening a screw hold one end of the link to the cistern handle.

Cistern fills with water very slowly - usually it should take about 2 minutes.

This problem is usually associated with water supply or the valve which controls the water flow into the cistern, suggested causes are:

  • If the cistern has always been slow to refill and the cistern is fed from a water tank, the problem is probably due to the wrong type of valve nozzle being fitted. Two nozzles are usually supplied with cistern valves, one for where the valve is fed from a header tank, the other (with a smaller hole) for where the valve is fed directly from the water mains - if the mains type of nozzle was fitted at installation, the cistern will take a long time to fill.
  • If the problem is new or has gradually worsened it could be:
    • Low pressure in the water pipe to the cistern - this could be a valve which has not been fully opened or an obstruction in a valve or pipe. Check all the valves in the pipe run, closing and then reopening each valve may clear any obstruction.
    • The valve on the cistern may have become partially blocked by much or scale in the water supply. To clean the valve, turn off the water supply and then dismantle and clean the valve.

Flush does not clear pan:

When a cistern flash fails to clear the pan, the problem is likely to be one of the following:

  • Only a half cistern of water has been flushed - this applies where the cistern is a 'half and full flush' type. If the cistern is this type,check to ensure that everyone using it is aware of how to use it correctly, i.e. the handle needs to be held down during the flush to obtain a full flush.
  • The level of the water inside the cistern may be low, it should be about 12mm (half inch) below the overflow pipe. The higher it is, the more water will be flushed down when the handle is operated thus increasing the chance of cleaning the pan. If necessary, raise the water level by adjusting the float as previously described for cisterns not flushing properly.
  • There may be a problem with the pipe from the cistern to the pan - check that it joins the pan squarely and that it is not obstructed. Also check that the rim of the pan is level side to side and back to front using a spirit level. The water entering the pan should run equally from around the rim.
    This is only likely to be the problem where the cistern/pan has just been installed or replaced.

Water coming out of the cistern overflow:

This problem usually indicates a fault with the ball valve or the actual float which controls the water going into the cistern, probable causes include:
  • A worn valve washer - this will stop the valve completely shutting off the water inflow, it may take a period of time (overnight or even days) for a slight leakage at the valve to raise the water level enough to overflow. It may be that normal use will 'hide' the problem and it may only become apparent after the cistern has been left unflushed for a long period. If you return from holiday and find the overflow dripping, don't panic, returning to normal use will appear to make the problem go away. On most types of valves, a new washer can be fitted, see illustrated guide for replacing the washer in a slide valve.
  • Water level set too high, the problem will probably have existed ever since the valve/float was last adjusted.
    The water inside the cistern should be about 12mm (half inch) below the level of the overflow - if the water level has been set too high, the excess will go out of the overflow pipe. The level of the water should be reduced as described above - to lower the water level, the float needs to be adjusted down, which may be hard with the float supported by the water, so flush the cistern to make adjusting the float easier and check the water level after the cistern has refilled.
  • If the cistern is fed directly from the mains, the incorrect type of valve nozzle could be fitted in the valve - the problem will have always existed since the valve was fitted.
    The valve may not be shutting off completely the water supply if a tank type valve nozzle was installed rather than a direct mains type nozzle - this has a smaller hole.
  • The movement of the float, or arm, could be restricted inside the cistern (possibly rubbing on the side of the cistern or the syphon assembly) this can prevent the valve from shutting off properly - where a solid brass arm connects the float to the valve, the arm can usually be bent sideways so that the arm and float move freely, where the float arm is plastic, it may need to be reassembled.
  • The float could be damaged (i.e. leaking) so that it sinks lower in the water than originally - a replacement float will overcome the problem, spherical float are usually easily to find and fit, replacement non-spherical floats may be harder to locate.

Water on the outside of the cistern:

Water all over the outside of a cistern is usually condensation. Condensation will occur where warm, moist air comes into contact with a cold surface. Each time that a cistern is flushed, the water entering it may be colder than the room temperature, so condensation will form.
There no way to completely prevent this although it may help to:

  • Increase the ventilation in the room, this may reduce the amount of moisture in the air.
  • Avoid doing things which will increase the moisture, such as drying clothes etc in the room.
  • Decrease the temperature of the room.
  • Wrap the cistern in thin expanded polystyrene insulation (as used behind wallpaper) - this may help but does not look very nice unless the cistern is concealed.