Central heating systems typically include a'header tank'which fills from the mains and tops up the system when evaporation lowers the water below a predetermined level, hence maintaining a substantially constant volume of water in the system. Problems occur when there is a sudden leakage somewhere in the central heating system e. g. a pipe bursts. When this happens, the water level in the header tank falls, this is detected by a ball cock valve which allows mains water into the header tank and then into the central heating system. Thus water continues to leak from the pipe until the burst is discovered and the mains supply is switched off. This often results in a flooded house, factory or office.

An object of the present invention is to provide a means of substantially cutting off the water supply from the header tank when a system leakage occurs, thus minimising the escape of water.

According to one aspect of the present invention, a fluid storage system comprises a container for fluid, the container being provided with a fluid outlet which would in normal use be below the fluid level, a fluid inlet and means for closing the fluid inlet in response to the level of fluid in the container, a float member which floats in the fluid, a plug supported by the float member, and a linkage between the float member and the container which allows the float member to rise and fall with the level of the fluid.

According to a further aspect of the present invention, a method of minimising fluid leakage from a fluid storage system which includes a fluid container with a fluid inlet and a fluid outlet, comprises providing the fluid container with a float member linked to the container and supporting a plug, such that in the event of a sudden loss of fluid through the fluid outlet the float member moves with the flow of fluid, dislodging the plug which will then substantially block the fluid outlet substantially preventing further loss of fluid through the outlet.

Once the fluid outlet is blocked, the level of fluid will rise to its predetermined level at which point inflow of fluid through the inlet will stop. The advantages of the present invention are that the modification required is cheap and easy to install and in the event of a water leakage, the present invention will minimise water loss and water damage.

Preferably a leakage indicator is also incorporated to give a visual and/or audible warning that a leakage has occurred and that the plug is in place in the outlet. This could be a battery operated pressure sensitive L. E. D unit linked to a visual display e. g. in the vicinity of the central heating control board. Once the leak has been mended and the plug/float member replaced, the system can be made fully operational again.

The float member which may e. g. be made of a plastics material, can be linked to the container by various means e. g. a separate hinge or a hinge integral with the float member or container, or by means of interlocking male and female components on the float member and container. Preferably the materials used for the plug, float member and linkage are resistant to attack from the fluid in the system. The float member may float on or below the surface of the fluid.

The size and shape of the plug depends on the size and shape of the outlet.

Preferably the plug is covered with a resilient material to promote a good seal with the outlet. The plug must be sufficiently heavy to sink once it is dislodged from the float member. For example it may be spherical and may consist of a metal core surrounded by resilient rubber.

It will be appreciated that certain features of the invention which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are for brevity described in the context of a single embodiment, may also be provided separately or in any suitable combination.

An embodiment of the present invention will now be described with reference to the accompanying drawing in which Figure 1 is a schematic representation of a central heating system. The sealed system consists of a tank 10 often referred to as a'header'tank, containing water 11. The tank 10 has an outlet 12 connected by a pipe network 13 to a boiler 14, pump 15, venting pipe ('expansion pipe') 16 and radiators 17.

The tank 10 has an inlet 18 connected to the water main which is usually closed by a ball cock 19. An overflow 20 is also provided. A float member 21 consisting of a rigid plastic panel is linked to the inside of the tank 10 by means of a hinge (not shown) made of stainless steel or plastic and floats on the surface of the water 11. Supported on the top surface of the float member 21 is a plug 22 consisting of a metal ball surrounded by resilient watertight rubber. Attached to the underside of the float member 21 is a pressure sensor 23 connected to a visual and/or audio warning device 24.

During normal operation of the central heating system, the volume of water 11 remains fairly constant. Any minor loss of water 11 by evaporation results in a very small and gradual lowering of the water level. The ball cock 19 then opens and allows mains water through inlet 18 until the predetermined level is again attained. During this operation the plug 22 remains on the float member 21. In the event of a sudden loss of water 11 from the system e. g. should a pipe burst, the level of water in the tank 10 suddenly drops, the unhinged free edge of float member 21 dips with the water level, and the plug 22 rolls into the water 11. The flow of water 11 through the outlet 12 carries the plug 22 with it until the plug 22 lodges in the outlet 12. This action blocks the outlet 12 so that substantially no more water 11 can escape and hence the volume of water which can escape through the burst pipe is limited. Water 11 is allowed into the tank 10 by the ball cock 19 until the predetermined level is again attained. The. pressure sensor 23 detects that the float member 21 has moved and transmits a warning signal to visual/audio device 24. Without the plug 22, water 11 would continue to escape through the burst pipe until the burst was discovered and the tank 10 would continue to be filled with water from the mains as water 11 escaped through the outlet 12. Such a large volume of water would cause significant damage to property.