Storage Cistern and Expansion Pipes


The storage cistern is also used as a form of safety valve for the hot cylinder. Heated water expands, so an expansion pipe must be fitted to the cylinder to accommodate this. Hot water must not be contained, for this could be dangerous.

The expansion pipe is taken from the crown of the cylinder via an offset fitting and curved over just above the cold cistern to provide the necessary hot-water vent.

The pipe should never be allowed to dip into the cistern, for this would set up a siphonage circulation and pump hot water through nearly every tap in the home!

Changing the old cistern involves a major shut down in domestic water services, so plan carefully for the minimum dislocation and make sure that you are equipped with all the materials and tools needed.

Shut down the supply stopcock and open taps and any drain cocks, to drain away most of the water. As outlets are usually located at about 75mm above the bottom of the cistern, this means that the residue of water will have to be baled out.


Fittings are usually easily unlocked, with adjustable spanners, where these are of the conventional compression type. Some fittings, used with iron pipework, may be heavily corroded and may have to be heated with a blow torch to expand them before removal with a large wrench.

One component which is frequently reusable is the ball-valve assembly. Sometimes the float ball becomes punctured, waterlogged and, therefore, ineffectual. The ball can be simply unscrewed and replaced.

It is sound practice to complete as much as possible of the replumbing of a new cistern before fitting it. If this can be done before putting it in the loft, it will make things a lot easier from a working point of view.

If a metal cistern is used, with consequent risk of corrosive electrolytic action, a suitable copper-to-galvanized metal connection should be used to separate the two metals.

The hole to fit the ball-valve assembly should be about 75mm below the top of the cistern and be slightly larger than the threaded valve stem. The hole for the overflow should be about 20mm below this point. Outlet connections are located at about 75mm up from the cistern bottom.

Cutting holes

Holes are made by marking the position with a centre punch and then using a hole cutter or a large auger bit to make the hole, centring on the punch mark to prevent the cutter from slipping.

There are two types of hole cutter-one has a number of interchangeable blades of various sizes and the other an adjustable cutter on a bar. Both have a twist-drill centre, which makes the pilot hole and, at the same time, provides a pivot point.

A hand drill is better to use than a power drill, since plastic heats up and becomes difficult to drill at speed. Use a file to remove any burrs left by drilling.

Holes can be made more laboriously by marking the circumference of the hole and drilling round, at intervals, with a small drill bit, until the hole is cut. The segments left can be trimmed off with a sharp knife or keyhole saw and the hole then cleaned up with a file.

Ball valves

Ball valves have two loose nuts on the stem; these go on either side of the wall of the cistern and allow adjustments to be made to the amount of projection of the stem. Another type has a single nut fixed on the outside cistern wall.

Plastic or fibre washers are fitted on either side of the cistern wall, before the fitting is tightened up, to ensure a leak-proof joint-though water cannot usually rise to this height.

Once the ball valve is in place, a swivel compression ‘tap’ connector, containing a loose fibre washer, should be fitted to the stem. This ensures a water-tight joint when tightened. The outlet from the connection is joined to the rising-main inlet.

Tap connectors can be either straight or angled, to suit the nature of your pipework.

The ball ‘float’ simply screws to the threaded float arm. It is a good idea to screw an anti-noise pipe into the base of the valve to reduce the sound of incoming water.

This pipe projects into the water, introducing the incoming supply below water level.


Overflows are another form of safety valve; if they are working, they fulfil a vital function-preventing a fault from causing possible considerable damage to the fabric of your home.

Overflow fittings can be made in either plastic or metal. The easiest to use is the plastic ‘push-fit’ variety, where a piece of pipe simply slots into a socket-ended section.

The overflow must be fitted to allow a slight continuous fall. The outlet point should be located so that it is clear of obstructions and where you can quickly spot it. Avoid positioning it where it can saturate any part of the fabric of the house.

Filling up

The cistern, once plumbed in, should be adequately supported beneath before it is filled. PVC cisterns can be placed on two or three sections of 100mm x 50mm timber, set across the joists. GRP cisterns should be supported by a continuous piece of material, such as 19mm blockboard.

Where capillary fittings are used for making connections near the cistern, take great care to protect the sides from the effect of heat.

Before filling the cistern, check carefully that all joints and connections are properly made. Check carefully for leaks during filling. If these occur, shut off the water and drain down the cistern. Never try to tighten up joints with water in the cistern; you may rupture it and cause a flood!

The ball valve is adjusted when the cistern is almost full. This is set to ensure that the water level is at least 25mm below the overflow pipe. You may have to bend-very carefully-the float arm to get the setting correct. With some patterns of valve, you merely adjust an alignment screw.

Test the operation of the ball valve, by drawing off a small quantity of water, and then observe the refilling and supply cut off.

After about a day, check the system carefully to establish that no joints are ‘weeping’.

Clean water

In modern building practice, roofs under tiles are felted to keep out dust. In many older homes, the loft becomes a dust trap. It is wise to make a lid for the storage cistern if one is not supplied.

This may be made from blockboard, chipboard or from various types of building board. If water is likely to affect the material, paint it. Make a hole in the lid to admit the hot-water vent pipe.

Lofts should be insulated against loss of heat, which makes a cistern vulnerable to freezing. This, and all related pipework, should be lagged.

No loft insulation material should be placed beneath the cistern. This is to allow heat from the house to rise and keep the storage water from freezing.

10. November 2011 by admin
Categories: Featured, Handyman Tips | Tags: , , , , , , , , , | Comments Off on Storage Cistern and Expansion Pipes


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