Lavatory cisterns - common problems

Below are a number of common problems encounters with cisterns and lavatories.

The first question you need to ask is "has this problem just appeared, has it got gradually worse or has it always been there ?", the answer should guide you to whether something has broken, worn or possibly been wrong since installation - this should help you discount some suggested causes.

Cistern does not flush when handle/chain is operated:

  • If a syphon type of cistern has never flushed properly, the likelihood is that the water level is too low - it should be about 12mm (half inch) below the overflow outlet. To correct this, raise the height of the float, the method depends upon the type of valve/ball fitted:
    • On some set-ups there is a hinge in the arm between the valve and the ball with a lock nut/screw - loosen off the nut/screw and adjust the hinge.
    • Other systems have an adjustable screw at the valve end of the arm (normally with a lock nut), release the lock nut and adjust the screw as necessary to raise the float.
    • The final arrangement is where there is a solid brass rod between the valve and ball without any adjustment; in this case, the rod needs to be physically bent. To do this, firmly grip the rod in both hands, hold the hand next to the valve still (so as not to put any pressure onto the valve) and use the other hand to bend the rod up a small amount to increase the water level.
  • If a linkage has become detached within the cistern, this should be fairly obvious as the handle/chain will loose its normal 'feel' - i.e. the handle or chain won't return to its normal position. Most linkages which have come loose can just be refitted and tightened after removing the top of the cistern.
  • If the cistern is a direct action type syphon type, the flexible diaphragm on top of the perforated disc may have become torn. If this has occurred, the syphon needs to be removed from the cistern the disc assembly dismantled and a new diaphragm fitted - although diaphragms vary in shape and size, replacements are usually readily available at DIY or hardware stores.
    See this page for details of how to do it.

Cistern fills very slowly - normally a cistern should fill within 2 minutes.

This is a problem associated with the ball valve which fills the cistern with water, possible causes include:

  • If the problem has always existed:
    • The wrong type of valve nozzle is fitted, a mains valve nozzle fitted where the valve is fed from a water tank - most valves are supplied with both nozzles, the appropriate one needs fitting at the time of installation.
  • If the problem is new or has gradually worsened:
    • Low water pressure in the feed pipe - either a valve has not been turned fully on or there is an obstruction in the pipe.
    • The valve itself may have become clogged by scale or muck in the water supply.

Water comes out of the cistern overflow outlet:

This is a problem which can be normally be traced to the ball valve or float which control the water entering the cistern, possible causes include:
  • A worn valve washer not completely shutting off the water supply, most types of washers can be replaced, see this page for replacing washers in slide valves.
  • Incorrectly set water level, the problem will probably have existed since the valve was fitted or last adjusted.
    The water should be about 12mm (half inch) below the level of the overflow, if it is very near the overflow outlet, the water level can be reduced in a manner similar to adjusting for low cistern water levels as described above but remember that to lower the water level, the float needs to be lowered - flush the cistern after adjusting the float so that the water will fill be the new level.
  • The wrong type of valve nozzle is fitted to the valve if fed direct from the mains.
    The problem will always have existed since the valve was fitted.
    If a tank type valve nozzle is fitted instead of a direct mains nozzle (the latter has a smaller hole), the valve may not be completely closing off the water supply.
  • The ball float is restricted in its movement (possibly catching on the side of the cistern or the syphon assembly) thus not closing off the valve properly - ball floats with brass arms can normally be adjusted sideways to clear everything, ones with plastic arms may need reassembly.
  • The ball float is damaged (i.e. leaking) so that it is not riding as high in the water as previous - replacement floats can normally be easily fitted although replacements for non-spherical floats may be harder to find.

Flush does not clean pan:

Assuming that it's not a particularly dirty pan (sorry!!), the problem is probably one of the following:

  • First of all, check if the cistern is a 'half and full flush' type. If it is, check to see if everybody using it knows how to correctly use it, i.e. hold down the handle for a full flush.
  • Check the water level in the cistern, it should be about 12mm (half inch) below the overflow pipe. The higher it is, the more water will be flushed down the pan and the more chance there is to clean it. Adjust the float as described above for low cistern water levels.
  • Check that the down pipe meets the pan squarely and that it is not obstructed. Check with a spirit level that the rim of the pan is level side to side and back to front.
    The water in a flushing pan should run equally from around the rim.

Condensation on the outside of the cistern:

This is not a fault, as with all condensation it occurs where warm, moist air comes into contact with a cold surface. Every time the cistern is flushed, it is filled with water which will probably be cooler than the room temperature.
Possible remedies include:

  • Improving the room ventilation to reduce the moisture in the air.
  • Reduce the temperature in the room.
  • Avoid drying clothes etc in the room.
  • Insulate the cistern using thin expanded polystyrene (as used under wall paper) but this does spoil the look !